1978 GMC K25 driveline swap

[THI]

I am fairly new to this section, had a '70 Suburban and several K5's that are now in someone else's possession. I have had for several years a 1978 Chevy C20 Camper Special with a slide in camper and just purchased a 1978 GMC K25 to use at my acreage in Michigan's Upper Peninsula. It will be used as a work truck and I need to do some updating over the winter so I can get it ready to take there.

It currently has a 400 SBC/TH400/NP203 combo that has done a really good job of preserving the underside of the truck - it all needs to be pulled and re-gasketed at a minimum. I have laying around a 350 and a 327 that both are fresh rebuilds, a fresh rebuild on a TH400 and a pass drop NP241. I am considering just replacing the entire driveline with the 350/TH400/NP241 combo but have two hurdles to overcome. The current NP203 is a stationary yoke and the NP241 is a slip yoke.

The front axle is the stock Dana 44 and rear is the stock 10.5" 14-bolt. I basically have two questions. If I put a Slip Yoke Eliminator Kit on the 241 will I have any issues with the rear driveshaft? Cannot find exact length on the combos to know how close they are. I may be able to get my hands on a driveshaft from a 3/4 ton that has a slip yoke used with a 208/241. My question here is I have no plans to lift this vehicle, but it will be used on an 80 acres plot that is very hilly - would I have any issues with the slip yoke in this scenario?

Thank you in advance - tom

[MJN]

I would suspect you wouldn't have any issues on hilly terrain with a slip yoke- they've been used on pickups, Jeeps, etc. Why switch to the 241? If you already have a TH400 in there- why not keep the NP203 and not worry about driveshaft length or having to install a slip yoke eliminator? Is the 203 bad (besides being heavy)? You would also benefit from installing some lock out hubs if you swapped in the 241 unless the 203 you have currently has already been converted to part time and you have hubs.

[THI]

I already have a fully rebuilt TH400 for the NP241 which is also completely rebuilt that are ready to drop into a chassis, I sold the 1980's K5 that I was going to drop them into a little over a month ago and the new owner did not want a driveline with it, so I have these laying around my shop. I was about a week from dropping the engine/trans/t-case into the K5 when it was sold so the rebuild on these items is recent with no miles.

The TH400 and NP203 that are in this truck leak and at a minimum need new seals to stop the leaking. Same with the engine - they are over 40 years old! I would rather put in a trans and t-case that I know their condition since I need to pull what is there to reseal them anyway. The 203 was converted at some point in it's life, previous owner not sure when as it was done when he purchased it - it does have manual hubs.

[1976gmc20]

Just me but if I was going to be using it hard I would prefer an iron transfer case, preferably the NP205.