Whew! That was not nearly as nightmarish as I expected- and I discovered several bonus things in taking it apart:
1. The rims for the truck are front and rear (they're a set, but slightly different shapes), and whoever worked on it last put the rear wheels on the front, and the front on the rear- which is why they wouldn't fit over the hubs- the fronts aren't meant to fit over the rear hub.
2. The rear hubs (which were too big to get the rims over) have a kind of cap-ring on them- that's the part that was too big. Imagine a washer with holes in it for the bolts that hold the axle in place, which sits on top of the face of the axle itself. I was expecting what's shown here
http://chevy.oldcarmanualproject.com...4ctsm0412.html , but it turned out I could yank that cap piece, pull the wheel off, and leave the axle be. YAY!
3. It looks likely that if I pull the rear drum, I will have to yank the cap again (bummer)
4. And, lastly, apparently after leaving the truck sitting for a couple of months, the right front drum brake has locked up. Jerk! I assume I can get down there and back it off... it won't even roll right now without making... mmm... how would I call that- crunching, spoon in the disposall noises? I backed it up about 2 feet and decided that was a no-go.
Thanks again everyone for the help and info. I may just get this thing roadworthy!