Sounds like there isn't much hope in it running. Would swapping the body over to a running truck/van be viable, or would taking the drive train out of the donor and putting it into this make more sense?
Swapping just the body to a modern chassis would be awesome - better brakes, frame, steering, everything. A drivetrain-only swap would maybe be easier, but not net you as much in the end IMO.
I wonder how close that would be to an Astro Van wheelbase?