On my car.... With a stock width rear end, 7" wheels with a 4-1/4" backspace is dead centered in your usable. I'm running 15x8's with 4-1/2" backspace, which moves the wheel 1/4" outboard from centered. A 255/60 should fit, but a 275 will be hit & miss. I see that sputnik is running them, and I'm very interested in the pictures he posted up. I think from car to car, though. results may vary with 275's.
Just to clarify, In the post where I talk about the 275/60r15 drag radials I state that for that combo I had a Dana 60 custom made that is 1 inch narrower than the factory rearend and be able to use 15x8 wheels with a 4.5 inch rear spacing.
The pic with the 15x7 magnum wheels the car has 255/60r15 tires and those pics are with the original stock width rearend.
