Should go to a museum.
No legitimate way to register it, it doesn't have a VIN. And a single VIN plate won't do the trick, it won't have VIN numbers anywhere, all of the normal locations for VIN stamping will be blank. And of course, even if you did basically "re-body" the thing, well, it just became that other car, and the history of the body is negated.
Building it would be a waste even if you could get it registered legally, because at that point its just another '74 Barracuda.
Definitely a cool piece, but pretty useless to anyone other than a museum. Owner should donate the thing and use it as a tax write-off, probably the only way he'll see anything close to what he's asking for it.
