Jim,
Sorry to hear about this! It probably goes with out saying, but try not to move the truck until you get everything cleaned-up: the engineers tried to design these axles with drain-holes and such to drain gear-oil out of the backing plate without soaking the brakes, but some might have gotten inside, and moving the truck might spread that oil around & over the brake shoes, ni which case you'll need to replace or re-line the shoes.
The shop manual does cover this thoroughly; I would suggest pulling the axle (wheel on the ground), then the wheel, then the brake drum (removing the two counter-sunk screws), then you can work on pulling the hub. Stripping everthing off the hub minimizes the amount of weight you'l be wrestling with.
Once you get the the hub off, pull the brake shoes off so they're not in the way and don't get greased if they haven't already. Then you can clean-up the grease and gunk; if you haven't done any brake work, this is a great time to replace your rear wheel cyls
, they should still be available through NAPA, Raybestos, or Wagner; also, while cleaning up the backin plate, look around the axle stub, where it meets the backing plate for some sort of drain hole: there's usually a tin collar that's supposed to catch any leakage from the hub seal and divert it through this hole and let it drain on the outside of the backing plate, hopefully keeping it off the brake linings!
Also, check the rear axle vent, which is a hollow, capped bolt, usually the one that holds the brass brake junction block to the rear axle housing. After cleaning that dirst away from that area, remove that bolt and see if you can blow air through it; if not, give it a soaking in gasoline or carb cleaner, until you get air to pass through it. If it's clogged, when the gear oil in the rear end gets warm, it can get forced past the seals, no matter how good they are.
Good luck!
Just keep that torch away from my collection as well as yours from now on. 