Do your research well or it can get expensive - there are at least 3 axle tube flange bolt patterns along with the different bearings that they use as well as at least that many axle shaft protrusions. My rear diff is a smooth back '57, but like all of the very early versions through, I believe '61, has a "non standard" axle protrusion. I used a small bearing flange Wilwood setup then made up the proper spacers to fit the calipers to center of the rotor