I know that when I have the rear end narrowed - my priorities will be to get the width correct and to make sure the pinion aligns. We played around with axle lengths on the last two rears we had done to even out tire clearance in the wheel wells. If we ever swap rear ends in the Roadrunner we'll probably do the same. When we measured for new tires/wheels the other day we found about a 5/8" difference from side to side.