1978 K2500 LS swap with a 4L80E

[THI]

Three years ago I started taking apart my 1978 GMC K2500 originally for Arizona. I found the not so original with cracked heads, a crankshaft that looked like it went through a war zone (chunks out of the counterweights), cracked housing on the not so original TH400 and an NP203 that looked like the Exxon Valdeze. To say this truck was "run hard and put away wet" is an understatement. I bought it for the solid body (with a really poor paint job) and clean frame. Un fortunately is sits in the same condition as it was 3 years ago - engine/trans/t-case gone, all the front sheet metal off (fender and inner fenders need replacing).

Right after I got the truck apart and was looking at what engine to put in it, I found out the hard way that I had a very large blood clot in my leg when it broke loose and I had a heart attack - traced back to the COVID shot! Recovered from that after about a year, then tore my rotor cuff and am not recovering from that surgery. All this down time gave me time to consider how to power the truck since it needs a complete driveline anyway. I have an NP241C passenger drop t-case that has been rebuilt, adapters for both a TH400 and a 4L80E along with a 1985-1991 "W" crossmember that works with the adapters. I also have a rebuilt TH400 and do have access to a 2003 4L80E out of a K2500 HD which I am leaning going the 4L80E route. I have 2 LQ4 6.0 engines, one complete including accessories, and one block I am in the process of rebuilding.

I know the 4L80E is 1-1/2" longer than the TH400, and a lot of the LS engine swap mounts set the rear of the engine 1" forward. Since this truck does not have AC I am not worried about how to mount the AC compressor. My thinking is if I mount the engine 1-1/2" forward and use a 4L80E trans, my t-case and drive shafts will be in the correct position without modifications. The driveshafts I have are off a Military 1-1/4 Ton that had a slip yoke NP 208, I have replaced the Dana 44 front with a Dana 60 front and still have the original 14-bolt FF rear.

Not having done this swap before, should I be looking at the Dirty Dingo Slider Mounts for the engine to get the position I am looking for? Also, if someone has done a swap like this on a square body, what advice would you give me? I still have several more months to recover from my shoulder surgery, but want to move forward by getting things ready for when I am able. Thank you.

[LS short box]

Never done a swap like yours but I've had the drive shafts made as needed or LS swaps.
So if you want to keep your drive shafts and no AC maybe get the Dingo mounts. Bolt the frame/engine mounts onto the engine and move the engine into position as needed to reuse the drive shafts.
You may have to drill new frame engine mount holes. Not a big deal.
Depending on your lift (if you have one) you may need a CV rear drive shaft?

[THI]

No lift planned as my wife has RA and has hard enough time getting in a stock lift 4x4

[bigmoe]

I wouldn't worry about having to shorten your driveshaft. It's not that difficult or expensive for a local machine shop that does driveshafts to shorten and balance it.

[cdub2010]

I did the same swap in my '77 k2500 with 5.3 4l80e np241. I used dirty dingo sliders, psi harness & ecu. I reused a stock front shaft from a 3/4 ton suburban. I had the rear shaft made new with 1350 joints on both ends. There is no way I would ever use a th400 instead of a 4l80e, the overdive is so much worth it. My truck can cruise at 80 on the highway very smooth. It was money well spent. My stock 5.3 with 31" tires and 4:11 gears is more than enough power for my needs.

You will be limited in how far forward you can go with the engine as the engine crossmember will need to be swapped out or trimmed for the oil pan clearance. I cut mine and had no issues. Dont worry about max power from the 6.0 its fine in stock form. Id get your truck running and driving before you chase all hp's. Dont cheap out, do it right, use good wiring, check, clean or replace all your grounds. I used 87+ tbi tank with ep 381 pump stainless fuel line plumbing. I ditched the second tank for simplicity. Full stainless exhaust, I will ditch the cheap stainless headers for some hooker cast exhaust manifolds, in the spring. The chineese stainless headers have rusted real bad. Been 5 years of use, I love the truck, Ill never use a sbc or carb again. Mine wasn't a cheap swap but its reliable and fun to drive.

Good luck with your health and your project. Im one year out from brain and heart surgery. Im finally just starting to feel like finishing a few projects that have been sitting for a while as well.

[THI]

Thank you for the input, sounds like I am taking a good approach. Will learn on the swap on this truck so I can do an LS swap on my 1975 Laguna down the road.