i have 12" rims with 71/2 backspace weld wheels.running phoenix 11.5x29.5 which are actual 12x30.0. stock width rearend.the main clearance issue is to make sure the inner tub is flush with the frame rail and not to get narrow at the top.the left side which is usually tighter is the one to look at.if you move your spring perches a little it helps alot with clearance.you don't have to center the rearend but move it a little definately helps otherwise you may have to use a spacer on that side.