SM465 to 700r4: Different driveshaft lengths?

[Nick_R_23]

This is going to be quite the convoluted swap so feel free to bail if it gets too difficult to follow along

I currently own a 1987 Chevy V10 longbed that has been converted into a buggy. It’s been severely hacked up, including a bobbed frame and questionable spring relocates. However, the cab is rust free and in great shape, and supposedly the truck only has 47,000 miles on it total. The TBI engine is in good shape, I have a brand new Level 3 700r4 built for it, and a rebuild kit waiting for the working but leaky NP208. It’s a flatbed and the front fenders and core support and have been cut. I’ve thought about finishing the truck, but it’s more work than I think I want to put into it, especially since I don’t have time to go wheeling anymore.

A gentleman up the road from me has a 1984 GMC Sierra, either 3/4 or 1 ton, long bed pickup. It has a title, but the cab is pretty rusty. The engine, transmission, and transfer case are all missing, but the frame, axles, and bed/fenders appear to be all in good or usable shape. The truck is free if I go get it. It used to have an SM465, but I’m not sure what transfer case.

My thought process will be to make a good, usable driving heavy duty truck out of the two. Since my 87 is fuel injected, I would like to keep it that way. My plan would be to swap the 87’s cab, TBI engine, 700r4, NP208, and all EFI components (tanks, lines, harnesses, etc) onto the 84 chassis, and keep the 84 frame, suspension, steering, axles, front clip, and bed.

My main question is this: Will my driveshaft lengths remain unchanged? I have a brand new rear driveshaft in the 87. If I have to have new ones made, it’s not the end of the world, I’m just wondering what my chances are of getting away with just a conversion joint?