1970 C20 longbed stepside body swap questions.

[MaxxRazz]

I know this has been talked about a lot bit I have some questions that maybe some of you can help me with. Also going to be make this a build thread.

In the process of starting my swap. I have a 70 C20 longbed I plan on swapping the body onto the 02 Silverado 2500 duramax extended cab shortbed.

I know most people I've seen shorten the frame due to wheelbase differences.
Mine is about a 16.5" difference. I dont really have the capabilities to cut and weld the frame besides my harbor freight welder I can barely use.
My main questions is, has anyone gotten around this by either lengthening the bed or making any other adjustments. Just want to know all my options before I start cutting into anything.

Any other recommendations would be greatly appreciated on this build. Thanks

[MaxxRazz]

did some measurements this morning and i have exactly 15" to deal with. silverado wheelbase is 143 and c20 is 128.

was thinking of 2 options

1. extend the bed 15" not too out of reach. only 15" shouldn't look too bad

2. make a custom toolbox/storage between the bed and cab. has anyone done this? i think this would be a cool custom option

[Caddylackn]

There are a lot of other measurements and things to consider.

1. Check the back of cab to the center of the front wheel measurement between the two trucks. These may be different, and change how much you have to section to get the truck to look right. This could help tell you what the older cab would look like set onto the newer frame, if the frame is not cut.

I would place the '70 cab onto the newer frame, before I decide where the newer frame needs to be cut, or if you can get by without cutting it. It might make sense to section the frame under the cab, or section it under the bed.

2. The duramax tranny may be a lot bigger and require a larger trans tunnel fabricated, or using the trans tunnel off the duramax truck grafted inside the cab of the '70.

3. The diesel tanks may be under the side of the bed outside of the frame. That won't work with a stepside. Not many other places to put a tank then except inside the bed or the cab.

4. Check with your license agency, will this be titled as a '70 truck or the other newer truck? This would determine what your GVW would be on your title when you are done. I would hate to take a 10,000 # GVW truck and end up with a 7,000 # GVW truck on your registration when you are done.

5. Shortening the Duramax frame will be no picnic and requires professional quality welds for safety. I would hire a mobile professional welder to do the work, but get everything ready for him, disassembly, prep, including measuring and marking the areas removed. I would have them cut the frame, they may want to z -cut it. I would budget $500 and more for whatever parts needed.

6. what would shortening the frame 15" - 16" would do to the driveshaft. Will it be a two piece or one piece shaft after shortening?

7. I would consider mounting the '70 cab over the Duramax truck firewall and keeping the Duramax dashboard, pedals, ABS, and electronics and fuse boxes intact inside the '70 cab. That would save quite a bit of work I think.

i would consider just transplanting the Duramax drivetrain into your '70. I think this is the easier route. You will lose ABS and other safety features, though.

[72 tigger]

You’ll need to be able to weld and fabricate to do what you want to do-
“I dont really have the capabilities to cut and weld the frame besides my harbor freight welder I can barely use.”

[MaxxRazz]

I'm by no means a pro but I'll make do with what I have. I know I'm going to need to fab a lot on this truck but I'm just trying to stay away from any super heavy modifications like the frame besides mounts and any other bracing il l have to do. Did a bunch of measurements and I have just about 16" that will be between the cab and the bed. I dont think extending the bed is going to look good. I think my best option without shortening the frame is going to be building a storage/toolbox to fit in that space. I havent seen anyone do this and plan on making it flush with the bed and extending just the side step to reach the cab. Probably going to be a storage box across the middle and a cabinet on each side. This will also be used for air suspension mounting if i do decide to go that route as well.

And any help on fitting the firewall from the 02 would be great as well. I've seen it done without it and it doesnt look too terrible but I'm sure the 02 firewall would be easier for all the interior and mounting

[Caddylackn]

I honestly think you would be ahead if you started with a late model non-extra cab frame and moved your cab and your '02 drivetrain onto that. I bet you can find a '00 - '08 frame and cab from a gas 2 door that somebody already picked the LS3 drivetrain out of for pretty cheap or free. I see those on craigslist all the time with the motor and trans missing.

Plus there is no guarantee that your '02 frame is not bent, it looks like it took a hell of a hit.

[BigBird05]

That's just what I was thinking.

[MaxxRazz]

Got some work done yesterday. And picked up a new core support today from the junk yard. Plan on pulling the rest apart tomorrow and test fitting hopefully this week. Not sure weather to transplant the firewall from the 02 onto the c20 yet. Anyone have any advice for me? I dont plan on using much if any interior parts from the 02 besides the cluster which I can make work with the factory dash for now. And I know I should be able to mount most of the pedal assemblies and a few other things with little modifications.

[special-K]

I think you are going to want to shorten the frame. Take it on. The frame needs to be lengthened behind the axle for the 8' bed, doesn't it?

[MaxxRazz]

Originally Posted by special-K

I think you are going to want to shorten the frame. Take it on. The frame needs to be lengthened behind the axle for the 8' bed, doesn't it?

I am going to see how it looks when I test fit everything. The rear should be ok. I think the bed only hangs over a few inches so it should be alright. When I get the and cab test fitted I'm going to measure the gap and see what kind of toolboxes are out there to use between to fill the space. I saw some semi truck toolboxes that come up to the roofline so I want one like that but only to the top of the bed.