I'll bet there are quite a few rigs here with "random manufacturer's parts"
The Waggy is a good starting point, but the drivetrain is not going to be popular. I mentioned SBC with EFI because you can get it new from GM, as well as the trans.
Direct Connection would work as well, HEMI, or the crate 360's....
Of course, you may be a bit too close to this vehicle, I know I purposely avoid looking at vehicles I've sold because I don't want to see what butchery was done.
Whatever they do, if it is chosen to be the Stone Soup project, it will definitely be finished and not rotting behind a garage