1970 k10 Shortbox - 402 BBC Swap

[Gawdly]

I had a 72 short K10 with a 350/350 combo years ago, never should have sold it. But the time has come for another. I bought a 70 K10 with a 307/4spd a couple weeks after I found a nice rebuilt 70 402 motor and decided it was time for a Big Block shortbed truck.

I drove the truck around for a week and actually didn't mind the 4 spd but it leaks like crazy and I know they make fitting headers a bear. So I've been reading a ton while I've been tearing the truck apart trying to decide the best way to do this.



Here's what I think I know:
You can mount a big block in the stock small block location but will have to deal with clearance issues at the drivers side valve cover and the distributer (if HEI).

You can run the 4spd if you run stock BBC manifolds (with trimming) or Doug Thorley headers if you modify your Z bar and clearance frame rails a bit.

If you have a 350/th350/np205 truck, the swap is pretty easy if you do the BBC swap and swap in a 700R4 at the same time by keeping the transfer case in it's stock location and moving the front motor mounts (cross member) 2" forward to accommodate the extra length of the 700R4. This also gives the best firewall clearance.

Based on what I think I know:
I am planning on swapping in the 402 along with a 700R4 and a NP205.

What I think I need:
Auto Trans steering column (ordered)
BBC Motor (have)
Pulleys, fan, clutch, etc
BBC Radiator and fan shroud (ordered)
BBC Doug Thorley Headers
700R4 and converter
Advance Adapter 50-5900 (700r4 output shaft to np205, 27spline) (ordered)
NP205 27spline
Stock th350/np205 transfer case adapter (ordered)
transfer case shift lever

I have sourced the correct th350 to NP205 factory adapter from a 1970 K20. I have purchased the advance adapter 50-5900 700R4 output shaft. I have a quote from a local shop to build me a stout 700R4 for 4x4 using the above output shaft. I have the 402 BB sitting in the shop. I have an Auto transmission steering column.

Questions:
Will my Rockwell transfer case mount/tranny cross member work with the NP205? or do I need to source a NP205 mount/cross member?

What am I not thinking about that I need to?

[bluek5]

I think you have about everything covered. Not sure about the crossmember for the transfer case. One thing to consider is the sump on the oil pan. I have a 71 4x4 that has a 396, it was in it when I bought it. The previous owner has cut a section out of the oil pan to clear the crossmember. I am not positive, but I think a stock pan off of a 67-72 truck will work. Nice looking truck by the way I love that color combination.
Paul

[Gawdly]

The 402 I have decodes to a 1970 Truck, so I'm hoping the oil pan will work.

Oh... and my 4x4 above is actually a 1971, not a 70. I have a 70 2wd too, old habits.

[Gawdly]

Anyone know if the cross member/transfer case mount on a 4sp/Rockwell truck will work for a TH350/NP205? Same mount, interchangeable?

[CUSTOM/10]

The 221 cross member has about 1" less drop to it from what I recall. This will make your T/C hit the high hump cover. You might be able to use spacers to gain the 1" back, or get a cross member from a 70-72 truck that came with an NP205.

* If your truck is a 71 you should have the correct cross member ! If you set the cross member up-side-down on a flat surface it should measure 12" from the flat surface to the bottom edge of the cross member !
Gary

[Gawdly]

Awesome! Thank you for the info!

I made big progress today. Motor is out.



Tranny/transfer is dropped part way.



The adapter says "Rockwell" but the Transfer Case looks like a NP205 to me, correct?



I got stuck with the cross member dropped only half way. The upper brackets don't clear the bottom frame rail when dropped straight down. Is there a trick to getting the everything the rest of the way down? Do I have to lift the tranny/transfer and separate them from cross member then rotate the cross member to get it out?

Or do I grind the rivets off that hold the upper mount to the lower cross member and then use bolts when I reinstall? (Rivets shown below)

[bluek5]

That is a NP 205. When I dropped the transfer case out of my Blazer I removed the cross member first. Unless you want to jack the trans and transfer case back up and drop the cross member I would think that you will need to grind the rivets off. As I recall it was no easy task getting the cross member out. I think I had to push one side back and pull the other side forward. A couple of my trucks have the rivets replaced with bolts.

[CUSTOM/10]

I agree with BlueK5, it is an NP205, and the cross member should be able to be taken out if you unbolt it from the T/C adapter. It's tight but should come out. You just can't get it into the correct position with the T/C still attached.

Once you get it out measure your cross member as I mentioned above.

Not sure what you have for an adapter ?

Gary

[bluek5]

Any updates on your install? I am curious about the oil pan clearance. I have a 72 with a 454 that the previous owner installed. He flipped the cross member around to clear the oil pan and left the bolts out of the bottom after notching the cross member. So the motor is really only supported by the upper half of the cross member. I have another pan that I am going to try when I replace the cross member.
Paul

[Gawdly]

700r4 is built, found the th350 adapter I need, waiting on delivery of a 27 spline input shaft for my np205 and the rebuild kit.

As soon as those arrive, the transfer case goes down to the shop to be rebuilt and married to the tranny. Then it'll be time to position the drive train and see what works/doesn't. Couple weeks I'd guess.

[Gawdly]

Doug thorley says they don't have BB headers to fit our trucks so I did some more research and ordered a set of hooker 2463 headers.

27 spline np205 input shaft and rebuild kit arrived. Have to finish getting the tranny/transfer out, hopefully have that done tonight.

[engineer_gregh]

Great project! Subscribed.

[Tomahawk30]

Well I'll be... Look who's back!!! Good to see you caught the American Iron bug again my friend. Not that I hold the VWs against you, but you have to have SOMETHING with a V8 in it! Now I wish I was living in Boise again so I could come help you with it.

[Gawdly]

Originally Posted by Tomahawk30

Well I'll be... Look who's back!!! Good to see you caught the American Iron bug again my friend. Not that I hold the VWs against you, but you have to have SOMETHING with a V8 in it! Now I wish I was living in Boise again so I could come help you with it.

Holy... Kentucky? You were in john day last I knew! Hope you're doing well Jake! Ya, the chevy bug bit again. My Chevy vs VW ratio is nearly 1:1 now. Getting closer on this one, I should have my transmission/transfer back from the builder this week.

As soon as this one is back together I start tearing my 1960 Parkwood wagon apart.

[Tomahawk30]

Very cool! Ya, we moved to Kentucky in November. Kind of a wild hair decision, but it's been fun. Bought a big old Victorian home that we are restoring / remodeling. Unfortunately I had to sell all of my trucks before we moved so now I'm back at square one. Hope to buy my first 72 Cheyenne Super back eventually, but it's out of my budget again for now.

Looking forward to watching your builds!

[mechanicalman]

Originally Posted by Gawdly

I had a 72 short K10 with a 350/350 combo years ago, never should have sold it. But the time has come for another. I bought a 70 K10 with a 307/4spd a couple weeks after I found a nice rebuilt 70 402 motor and decided it was time for a Big Block shortbed truck.

What am I not thinking about that I need to?

Sounds to me you are on your way. The chart below shows about a 2 3/8" difference between the case length of the t700 vs the t350 measured from the place the tail housing would have bolted on. Not sure maybe you know that and just said you needed to move the engine forward 2 inches.

[67-4x4]

I am in the process right now of putting a 396 in a 67 and I moved everything up 2.5 inches forward shortened the front shaft had a new shaft made for the rear just the one that goes to the trans. Had to open the holes in the hump then redid those , also had to shorten the 4wd shifter . Used the original manifolds with proform motor mounts and used an oil pan from a chevelle to clear the cross member . You can use the big block fan shroud when you move it up

[Gawdly]

The plan is to mount the transfercase in the stock location and let that define where the motor lands. I had heard 2-ish inches forward, looks like it should be 2 3/8". Shafts, shifter, etc should all stay the same.

[mechanicalman]

Originally Posted by Gawdly

The plan is to mount the transfercase in the stock location and let that define where the motor lands.

Shafts, shifter, etc should all stay the same.

That's the beauty of doing it your way.

[gregbr]

Subscribed! Thinking of putting a BB in the 67 4wd. Keep up the great work! Greg

[Gawdly]

Finally got my 700r4 and np205 back from the trans shop today... Took tomorrow off to dive into this project. Would love to have engine/tranny/transfer bolted in tomorrow so the lifting's over. Wish me luck.

[Gawdly]

Engine and tranny are mated and sitting roughly in place. I moved the engine cradle 2 3/4" forward and left it unbolted for now until I can get everything exactly where it needs to be. Transfer case is mounted to cross member and is half way in. The cross member is dropped ~8" sitting with the upper mounts on the inside of the lower frame rail. Sunday I will move the case and member back a couple inches, tilt the engine/tranny back to get the tail shaft at roughly the same height as the transfer. Then tilt the transfer and attempt to mate it to the tranny.

From there, I will lift the transfer and crossmember into it's factory position and mount it, sliding the engine/tranny forward/back as needed. Once it's all mated and sitting with the transfer mounted in the factory spot, I'll drill the new holes for the engine cradle.

I bought some prothane small block mounts for this swap. I must have fought the threads in those things for an hour.

In the good news department, oil pan fit great with no modifications. I believe it's an original 1970 402 truck pan.

[Gawdly]

It's in.
Engine landed roughly 1 3/4" forward with the transfer mounted in the stock location.
Drive lines are back in and won't need modified.
Thank god the heavy part's over.

I got the headers in too. Had to clearance lower frame rail on pass side about 1/8". Had to clearance rear of engine cradle on driver's side about 1/4". And I had to beat the passenger side header in about 1/2" where the tubes are welded to collector in order to clear the upper shackle bolt head.

This weekend I'll start on the interior stuff... steering column replacement, pedal assembly replacement and tranny hump replacement.

[gmc 2500 4x4]

im doing a 402 into my '69 gmc 4x4. i was wondering about the oil pan also, without moving engine 4ward. i can handle the firewall issue but need to know what i might need for a pan

[Gawdly]

Originally Posted by gmc 2500 4x4

im doing a 402 into my '69 gmc 4x4. i was wondering about the oil pan also, without moving engine 4ward. i can handle the firewall issue but need to know what i might need for a pan

I believe the pan on the 1970 402 Engine that I'm using is the original truck oil pan. It has at least an inch of clearance even at the tightest spots using the original small block engine cradle in my 1971 truck and prothane small block motor mounts (which are a little thicker than stock).

Get a stock truck pan if you can find one.