Well if your talking backspacing not offset, im not sure how they figure offset, i think zero offset would be a 8" rim mounted at 4" anyhow, I would use 6" rims up front, 4/2 backspacing, 4" inside 2" outside, but what does that do to the scrub radius, you could also go 3/3 you dont want to use a 8" wheel with a 8" tire up front... Id also use 10" wheels on the rear with a 12" tire, you could go as far as 8 but it would really make the tire tall and rounded... the 3/3 would give you 71" plus sidewall.. 10" wheel out back with a 4/6 "4 inside" offset would give you 70 plus sidewall...