The torsion tube does have the VIN number, right?
If you're going coilovers in back, you can do the same thing 911 owners do, they bolt on a heim joint plate for a torsion bar cover, then fabricate trailing arms and strengthen the shock towers to support the car's weight. Simple triangulation(like a Kafer bar) can really stiffen up the rear end.
I like Stan's front end idea, but I'd go with a Miata front end rather than the Mustang II. Ford Pinto DNA is WAY worse than VW, IMHO.