I used the front and rear diffs and 203 transfer case from a 1976 Blazer. It is a long time ago, but the swap just took time to piddle around with little stuff. I used a different pitman arm, but I can't remember what truck I removed it from.
The biggest part of the job was welding the spring pads and narrowing the distance on the diffs slightly to match the 55 springs on the stock frame. I also had to find a pair of 4" lowering blocks to raise the rear of the truck to be level with the front, because the diffs mount below the springs.
I have a Corvette power steering unit ready to install when I can get back to working on the truck
I am going to reconvert it back to a 2wd, but I have to get this garage finished and take care of some other critical priorities first.
Bob

55 Cameo 396 TH 400 with overdrive
65 Caliente conv
67 BB Caliente conv
67 Mercury 1 Ton
76 GMC 3/4 ton 454ci
84 Buick Turbo Regal