I'd go for option d) sell them both and buy a Celica
If you do want a Sprinter and the one you have is stuffed then by all means transfer all the good bits into the shell. It shouldn't take too long (couple of big weekends), especially if you are offering beer to your mates. You can cash in your rego to help with roadworthy and rego on the new one.
I personally wouldn't bother unless the engine and suspension and everything else is in good condition. You would be better off selling the lot and starting again with a decent car