If you do not really know the correct gearing for you. Would it be better to swap the axles if you could. I have a chance to pick up a complete set of axles out of a 66 V6 4.88 gears open. My front 27 has issues and the 30 I grabbed once upon a time has 4.10 gears. Seems about the same price to change the gears on my rear as it is for the set with 4.88 gears. Bad part is I feel like I will want/need over drive once they are in.