I do track the car with NASA and a local vintage group. So zero offset on a 7 incher means 3.5 inch of backspace correct? If that is correct I would be putting the face of the rim .5 closer to the fender/quarter than your set up. (3 inches wider, 1.5 inch more each side, backspace increased 1 inch.) So sound to me like from your experience I would have to switch to coilovers, run a 5 inch backspace, and roll the fenders. I can't switch to coilovers for the vintage thing so I guess this idea is out.