I think the best thing you can do when a project stalls is buy another one, and when that one stalls buy a third one. So I brought this 91 GMC home today. The plan is to pull the 350/4L60(?) out of it, swap in the 454/4L80 out of my 92 (and then throw that truck in the garbage), lower it, wheels and tires and paint. I don't expect the drivetrain swap to be too bad with both trucks side by side, and the body seems to be in pretty good shape so paint shouldn't be too outrageous. Probably just a simple drop spring/spindle/flip kit and cast wheels to keep costs down.
2024 Chevy Silveraydo 3500 Duramax
2007 GMC 2500 Duramax
1981 GMC C1500 454