If you have stock axle bearings and want to reinstall it, it is fairly simple. Punch the remaining roll pin out of the thrust block by placing a socket or something similar on the larger side of the thrust block and drive it out from the smaller side with a punch. Reinstall each side of the thrust block by sliding them into each side of the differential, small ends first from where the axles go into it, slide a new roll pin in from one side, place a large drift against the roll pin head from the side you just installed it from, rotate the differential so that it's sitting on the drift, take a center punch and punch the opposite side of the roll pin. This will cause the roll pin to mushroom out to hold both pieces of the thrust block together.
