my dad uses a case spreader and the ford rotunda set up tools. the kit from ford does a lot of their rear axles. sometimes they are found on ebay. the tool sets the pinion depth at zero depending on what shim is needed. then if you change gears, you just have to add/subtract the difference of the plus/minus on your new gears. he also puts the shims behind the rear bearing race so he does not have to remove the bearing from the pinion. he also used dummy bearings for the carrier to set backlash.