With the body off, now would be an exellent time to thougholy inspect the frame for issues, the brake lines, overhaul the suspension and drivetrain. With the engine/tranny out, acess si very easy to all of the lines and such. When I did mine, I replaces all of the lines, hard and flex, as well as a complete overhaul of the springs/kingpins. I found it easier to work on the suspension by supporting the frame on a sturdy pair of sawhoses (ours are very overbuilt) that allows one to drop the axles out as a unit, then work on them off the truck.
The drums, if in spec (about 11.030, max) and not out of round, should be able to be turned, as far as the hydraulics go, there are replacements available, I would just go with new. You'll want to do the kingpins and spring /shackle bushings at this time, too. Much easier to deal with without the weight of the body/engine on the frame. If you plan to keep the original engine, do the overhaul on it, and replace in the frame before reinstalling the cab, saves alot of headaches.
