I have a service manual set for the truck from the PO and have NEVER done a F250 rear brake job. The manual mentions a tool for holding the tire as the axle assembly is removed.
Surely someone else is a shade tree mech type and can shed a little light on the process, without dealer tooling in the garage. I'd like to get a look at things as the rear brakes have a very faint metal on metal sound all the time. And the E brake will not hold the truck even at idle.
If it's what I'm thinking, it's a sort of a dolly. They use those fixtures for big trucks since the tires are so heavy, especially with the brake drum and hub still attached. What I've always done is to jack it up and pull the tire, then unbolt the axle flange and slide out the axle. You'll need to have a catch pan under the hub as some gear oil will most likely come out. Then, you'll be able to see the locknuts that hold the drum/hub assembly in place. There are special sockets made to get these off, they usually run about 15 bucks or so at most auto parts stores. There's an alternative method which uses a big screwdriver and a hammer, but I consider that to be an emergency measure for when you absolutely have to get the hub off and have no access to the correct socket.
When you get the locknuts and locktab off, the outer bearing wil easily come out. You can then slide the hub/drum assembly off by hand without any special tools. It's heavy, but not too bad and is easier to manage than it would be if you were doing it with the tire still bolted to it. It can save you time to leave the tire on, but there's always the chance you're going to have to turn or replace the drum anyway, (especially if you're hearing metal-on-metal) and then you'll still wind up taking the tire off the drum.
That's tough to say till you get in there. If it hasn't been done for a while (or ever) replacing the hub seals is a good idea. If you want to do a complete brake job, plan on shoes and brake hardware, seals and locktabs. See if you have a local source for the bearings, wheel cylinders and even the locknuts so you can replace them if needed after you get it apart an inspect everything. Nothing worse than planning the job, getting everything you think you'll need ahead of time and then finding something you didn't plan on that just has to be replaced.
Last fall I did a whole brake job on my '68 F250 and replaced a whole bunch of stuff including the rubber brake lines and a couple of hard lines. I found a lot of stuff at closeout prices at rock auto. There was a lot of hardware that needed replacement, adjusters, wheel cylinders, return springs, etc. Do what Tiger Dan said to get the drum off. I'm over 70 and weigh 150 and had no trouble.