I am running a 10" wide rim with 325-50R-15 tires that have a 13.5" cross section. I can't give you the back spacing that you will need as I am using a B body 8.75 that has been narrowed 12". My rims have 3.5" backspacing.
I'm running ProStars, 15x4 in front, and 15x10 in back. The back have 3.5" backspace. My Dart is mini-tubbed, with the springs moved to the frame, and the 8.75 rear is narrowed.