For the rear, you won't be able to get the tires to tuck inside the fender lip with a 15x8" wheel with 4" backspacing. You'll need 4.5" backspacing. A 245/60/15 fits with no rub, and I'm fairly confident you could get a 255 to work as well.
For the front, a 15x7 wheel with 4.25" backspacing and a 225/60/15 tire fits well. You may get some rub if you bump up to a 235, but your results may vary depending upon your brake set up. My disc brake conversion kit pushed out the hub face .25" -.50" from the stock drum set up.