Is it still a SWB car, or have the trailing arms been changed?
The best market for this car if it is too modified to be returned to a street car I would think would be a correct 2.0L vintage race car. The 901 shop in Florida makes some nice composite early 911 rear quarters that would fix that aspect and changing the rear bumper back to the early style would be a good start I think.
Lightweight Rear Quarters