Im thinking about getting torque thrust 17x11's in the rear, and stuffing some 315/35/17 on them. What backspacing would I need to run in the rear? I know I would also need to roll the fenderlip to clear that tire. I did a search and came up with some numbers, but i'd like to get a definite answer, maybe someone has ran this size before. What can I do to get additional space in the rear?

I have 17 x 11 wheels with 315/35 tires on my 70 El Camino. Backspacing is 6 3/8". I did not have to roll the lips or trim the wheel well mouldings. The tire is about 12 3/8" wide at the sidewall.

I have 315's on my 68 w/ 9.5" rims and 5.5" bs. It is really tight on the inside.
I didn't have to do any body mod to make them fit. just bolt on.