Standard rebuild: replace diff balls and spur. Use 220 sandpaper and sand the surface of diff rings (you can sand and reuse the diff rings several times). During the inital building if you sand both sides of diff rings then if you had to rebuild or replace the diff balls/spur all you would have to do is flip the rings over.
If you are looking to upgrade the complete assembly Irrgang sells the complete setup (grahpite axles, spur, dif ball, diff ring and hubs $65) or separately. Most are using the D ring hub and axles. To balance wear of the rear bearing during maintenance swap them around, use the axle bearing on the diff hub and swap the diff bearing to axle if they are still good.