This might help as a starting reference point, I have a 70 cuda, I used 17x8 on all four wheels 4.25 backspace in front 235 55 17 Goodyear rsa & 4.50 backspace rear 255 60 17. I kept stock rear leaf spring, it gave me approximately 5/8" - 3/4" clearance from touching the rear fender & leaf spring. Hope it helps.
Andrew