I have a 82 K10 4x4 with a 350. It has a 6" lift on 35" super swampers. I am not to sure about all the specs of everything but I know it was a diesel and the owner before the guy I bought it from did all the work. I do not know what transmission is in it either, it has a H shift pattern (3 spd with overdrive) and reverse is branched off of the left side next to first gear. I know the clutch is done and I want to figure it out so I order the right parts. Thanks.

 

That sounds like a Ford early 80's model. I know, sounds nuts but I have to ask, does it have any numbers on the case? Is it a Heavy Duty type unit or is it regular duty? With mods done to it, you may not be looking at an all GM gear train.