The bearing stabilizer bolts are the two large bolts on the face of the cover which line up with the bearings on either side of the large pinion gear. The purpose of the bolts is to help keep the bearings from going egg shaped and torquing out of position under extreme loads.
One thing the directions do not mention is that these bolts are not sealed and gear lube will leak out of them over time if you do not seal them. Easy enough. Before installation, run the bolts most of the way in and apply some thread sealant or RTV silicone to the threads inside the cover. You can use the same RTV that you will use to seal the cover (black or gray is my preference). Then run the bolts back out so you can install the cover.
Apply your RTV around the mating edge of the cover and bolt it up in place. Do not remove the excess RTV until it is dry, otherwise you will make a mess of it. Once the cover is bolted in place, run the bearing stabilizer bolts down until they just touch the bearings. DO NOT put excessive pressure on these bolts or you will distort the bearing and cause premature failure. You want them just lightly seated against the bearing race. Tighten the lock nuts while holding the bolts in place so they don't turn.
Wait until the silicone cures, remove the excess with a razor blade or scraper and fill the differential with the appropriate gear lube.
