Wheel bearings aren't hard to change on these cars at all. Simply, those 4 bolts are all that hold it in. Their not pressed into the axle tube, but sometimes they get stuck. The bearing race, however IS pressed in. If it looks GOOD, leave it alone. If you do need to replace the race, a little effort and a pry bar usually pops them right out. A good dead blow hammer and a block of wood will put the new one in for you.
Removing the axle: Take off the wheel/tire. Then slide off the brake drum, you may have to back off the adjusters a bit. Now, slide under the car. Take off the cover. Spin the carrier until you see the small lock bolt that holds the BIG lock pin. Need a 5/16" SHORT (I use my 1/4" drive set for this, not much room for big stuff in there.) socket. Remove the lock bolt. Then remove the big lock pin. If you have a posi, there's a big "S" spring in there that needs to come out. Trust me here, they come out alot easier than they go back in, but still not difficult. Big scewdriver, small prybar will do the trick. Careful not to bend it. Next, push the axle IN from the brake drum side. Go back to the center section, remove the small "C" clip from that axle. Head out to the brake drum side, and slide that puppy out. Now you'll see the lock plate with 4 lock nuts looking at you. Bolt heads are behind the backing plate. Take out those 4 bolts (No need to even remove the brake shoes!) and you'll probably have the bearing laying in your hand. If not minor coaxing is all it'll need.
SORRY for getting long winded here!
As far as what's actually MAKING your noise?
Could be the outer bearing, could be the diff itself. Sounds like the center section to me. Best to make sure. If you take off the cover, and get all kinds of metal, or if the oil looks like Never-Seize, put the cover back on, fill it up with oil, and take it to your wrench. Setting up a rear end really isn't something for a novice to play with (no offense intended) But the axle bearing you should be able to handle with basic hand tools, and an hour or so.
Hope this helps you guys out!!! Good Luck!