The saddle is held in the truck with 14 bolts. Three 1/2" on the bottom on each side of the frame rail and four 3/8" on each side rail vertical surface. These four bolts on each side go thru the 1/2" spacers mentioned next.
The AD frame is 1 inch narrower (28.5") than the donor truck frame (29.5") so a 1/2" shim must be used on each side. I used 1/2" thick aluminum since it was easy to work with and had some left over from another project.
This is a dummy small block which I originally installed with the stock truck motor mounts, but found it was too low and the dampner was very close to the crossmember. I used some 2X3 mild steel tubing to raise it up. I made a mount to attach the steering box to the front frame horn, and due to the angle etc I think it took longer to build than install the saddle. Also visable is the six cylinder (3.40:1) rear from a 78 Chevy 1/2 ton. Note the spring perchs are still on top of the housings and need to be moved to the bottom. I used this rear since with the little 283 it works quite well. The 77 GMC (V8) rear from the donor truck was the very common 3.07:1 ratio and would probably work great with a larger 350 motor.
I've made some aluminum covers for the firewall, which eliminated having to weld up all the holes made for who knows what by previous owners. The rebuilt two stage master cylinder is now bolted to the booster, and easily clears the right valve cover. The square hole to the right is for the wiring harness plug from the original donor 77 GMC, the back (or inside portion) is the actual fuse block. The steering column is from the donor, with the upper CV joint and lower rag joint. I did have to lengthen the shaft several inches between the rag joint and CV joint, since the cab on the AD is further back than the 77 GMC. The shaft actually goes thru the inner fender splash shield via a oblong hole I cut in it. I'm using later model cast iron exhaust manifolds with plugged smog ports only because they were on hand. I would prefer the rams horn type if I had to go and buy them. Either type can be had with the alternator mount, and although not mounted here I made a mount for the tear drop type GM power steering pump, which resides just below the alternator.
Note the 1 1/8" sway bar from the donor truck fits if it's flipped over. One of the holes in the frame horn where the original shackle bushing holder was riveted on works as a mount for the half moon urethane bushing holder and the other has to be drilled since it's wider than the bushing mount.
The original shackles and bushings were completely worn out and were replaced with commonly available repo parts. I made some mounting plates to utilize the original shock mounts on the rear housing. Since one is forward and one is rear and the frame is tapered, they have to be of different lengths out from the frame rails. You can't just make two identical mounts.