I took this (my) response straight off another post a week or so ago.
There a PITA. Sometimes the stub shafts dont come out. You split the cases. To get the carrier bearings out its easiest to get the races out by putting the case halfs in a parts washer and it will expand and then beat them on the ground to get them out, or run a bead inside the race and flip it over and beat it out that way. Knock the pinion races out, new races in. pinion in and set the carrier in and bolt the halfs together, take out the vent plug, check backlash and pattern and adjust from there. NOt hard, just a pain.
Also, DONT run Genuine Gear, get Sierra Gear.