1972 GMC Farm Find LS Swap

['68 C10]

I've had this truck for almost two years now. Original 350/TH400/AC cab truck that I acquired from a gentleman that used it as a farm truck for several years. The original 350 had been replaced in favor of a crate 350 in the 80s. Needless to say, it has been a bit wheezy since. Still has a noticeable chop at idle but at times I couldn't tell if it was a perfect miss or the cam lol.

When the time came, I ultimately decided to go through with the LS Swap. I obtained a motor/trans/harness PCM for a gentle $900 locally out of an '01 Silverado. I preferred a pre-03 motor to have a DBC setup.

Here's what I'm working with. The truck has some rocker panel issues but other than that, there's really no other trouble spots. The patina is what sold me on the truck.

['68 C10]

Although I really wanted to attempt to retain the stock location AC compressor and mate it to the existing AC unit in the truck, I haven't read very many success stories so I ordered the CPP motor mounts and sheet metal perches for non-AC setups for more adjustability. Also purchased the tubular trans crossmember and trans mount. Down the road I'll delve into getting the AC back with a retrofit unit via Sanden etc etc.
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['68 C10]

Pulled the front end off, got the old lump removed, the perches bolted down, and the new setup stabbed in with the mounts. Aligning the motor took some fiddling, but ultimately got it mated it. The sliders make it really easy to adjust the motor's placement. It's currently sitting with the sliders all the rearward. Stock truck oil pan cleared the crossmember easily.

['68 C10]

For the exhaust manifolds/headers, I decided to go with Speed Engineering swap headers over the initial plan of LS3 stock manifolds. The fitment of them were really good, the flanges are nice and thick. I did use a set of GM manifold gaskets, as the supplied gaskets weren't up to snuff in my opinion.
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['68 C10]

Little bit of an "Doh" moment that was overlooked.

In the process of getting a high pressure PS hose made, I realized we forgot to remove the ground/positive wire ground on the driver side of the block. The seller of the motor had cut the battery cable harness and this was one of the victims. I'm not really looking forward to pulling the motor back up and/or removing the perches and sliders to solve this considering how fiddly it was to get the motor stabbed. Suggestions?
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['68 C10]

Got the fuel system plans sorted for using the stock in-cab tank.

Walbro 255lph inline pump with 3/8" barb to -6AN feed fittings.

Corvette regulator w/ -6AN feed and return fittings

The plan is to utilize the factory 5/16" '72 return on the sending unit, considering the return line size of the regulator is 5/16" as well.

I obtained a returnless fuel rail from the local Pick-A-Part and mated an EFI quick connect to -6AN fitting on it.

Now just need to run the braided lines and that issue is solved.
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['68 C10]

Seeing how the truck had a TH400 previously, I knew the truck was going to need driveshaft work. The local machine shop persuaded me to go with a 4" one piece aluminum shaft. The total to redo the two-piece with new UJoints, 4L60 Yoke, and shorten 4" was in the ballpark for a one piece. So the decision was made.
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['68 C10]

Got the harness rework done and back on the motor. Doesn’t look the prettiest but it’ll do. Next up this week is routing the fuel system and then hopefully firing the motor.
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['68 C10]

Got the fuel system sorted. Nothing special, external Walbro 255lph, Corvette regulator, return back to stock sender/stock tank, feed to the returnless fuel rail. Used all AN6 fittings and Nylon braided line. Was able to use existing holes in frame from previous fuel lines.
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['68 C10]

I got the throttle cable work finished as well. I was initially going to run a Lokar aftermarket unit, but was advised a factory GM truck 99-02 cable would work with some modifications. I trimmed (or should I say squared) the factory mount on the firewall with a box knife. Once that was mounted on the firewall I was able to install it with the factory bracket on the intake manifold. Inside, I cut the end of the factory cable, clipped in the pedal mount, and installed a cable stop I got from AutoZone. Works really great, pedal is right on the floor at wide open throttle.
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[evanhall19]

now im considering throwing a 72 sending unit in our tank, ive been pondering how to get a return line integrated into the old tank lol. good job so far! cant wait to get ours stabbed this weekend.

[72 tigger]

Nice work! Following along

['68 C10]

Rejuvenated the project now that its warmed up. Got the lowering shocks on.
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['68 C10]

Transmission fittings and braided lines ran to the trans cooler. I will eventually route the lines through the rad as well but for now this will work in order to fire the truck.
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['68 C10]

Lokar Trans linkage installed
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['68 C10]

Tuned out the VATS and got the truck to run. Wouldn’t find idle at first. Disconnected the MAF, and it dropped down to set idle. Cleaned the MAF with electronics cleaner and problem solved. Idles and revs good. Suspecting an exhaust leak somewhere but that can be tackled later.
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['68 C10]

Finished the painstaking process of removing the factory crossmember that once housed the carrier bearing. Ordered a Porterbuilt member w/o trailing arm ears. Had to cut the old member out in pieces and then grind/cut out the rivets.

Went ahead and removed the bed as well, after getting the crossmember out in order to easily swap in the lowering leafs.

Installed the driveshaft

Afterwards I took the time to clean up the frame and do some beautification to it with a wire brush and wheel and some black paint.
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['68 C10]

Got bed back on and bolted down. The 4” drop looks good at the moment but I’m thinking some lowering shackles may be needed.

Tackled the front suspension this week. Standard CPP 3” drop coils up front. Went ahead and replaced the worn upper ball joints. They were bad!!
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['68 C10]

Also decided since the front clip is off, I might as well stab the TSP Stg 2 Truck cam in........and thats where things turned for the worst. Might as well add new heads (2 exhaust bolts broke on bank 1 anyways), rockers, and lifters. Going to go ahead and replace intake gaskets and knock sensors while I’m there.
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[boynton]

did you buy that motor out of Houston area? looks like it took a swim. looking like a fun project!

['68 C10]

I bought it locally, here in the Panhandle where it’s dry the majority of the time. I’ve already placed an order with TSP for lifters, oil pump, gaskets and PRC Stg 2.5 heads. Might as well make some extra HP while it’s apart. Going to pull the heads and pan this wkend and check out the internals to see if the short block is even worth running.
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[boynton]

Originally Posted by '68 C10

I bought it locally, here in the Panhandle where it’s dry the majority of the time. I’ve already placed an order with TSP for lifters, oil pump, gaskets and PRC Stg 2.5 heads. Might as well make some extra HP while it’s apart. Going to pull the heads and pan this wkend and check out the internals to see if the short block is even worth running.
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Sounds like a good plan. Can’t wait to see it come along!

['68 C10]

Started the tear down to assess if there were any issues on the bottom end and the lifters. #8 cylinder did have some rust as well.
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['68 C10]

Several pads of scotchbrite and cleaner/wd40 later, its cleaned up good. Happy to find no pitting or gouges in any of the cylinder walls. Disregard the dark stuff at the end of the cylinder wall, just some leftover debris from cleaning the walls and deck surface.
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['68 C10]

15 of the lifters came out in good shape and I was starting to get a little disappointed I had torn down the top end of the motor...but #16 came out and validated my decision.
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