ok duster gang

15x8 wheel with 4 inch backspacing. You can just fit a mickey thompson 10.5x28 slick. It will just clear the leaf springs on the inside. I did also trim the wheel well lips just a small amount to make sure it wouldnt rub on them while turning.

275/65 street tires of almost all brands should fit with the same wheel configuration.

That is with stock location springs, i see you said you have offset shackles. Not a clue with that.

No idea of what you can run on the front. I know 185/65 fit, all i run is the skinnys up front.