First off it took me about 2 years of web research for the following info. No one need to go through this much work. I did it for part availability and safety, new drum brake parts are hard to find.
I used the front spindles and brake calipers from a 81-82 1500 GMC pickup. With this I had to reamed the holes (for a different taper) for the ball joints and rod end. Then I used the rotor from a 81-82 2500 GMC pickup. The studs on the rotor is larger the're 9/16" instead of 1/2".
Minimum rim dia. is 16" four all four wheels. If you have manual steering make sure you have at least 1" offset on the rim, this with keep the steering as easy as possible. You want to keep the tire pivot point (upper and lower ball joints and the center of the tire) in the center of the tire. Also be sure to follow the manual for wheel alignment. The caster should be ZERO or 1/8° positive, this is with an empty bed (unloaded). Set the camber and toe to match the maintenance manual spec.
For the rear axle I went to:
http://tsmmfg.com/Rear%20Disc/2629.html
I updated the rear studs to match the front. The rotor they provided has two set of holes. One for the 1/2" studs that they had to drilled. And 9/16" studs that the factory drilled. To keep all four rims the same you will have to remove the rear hubs to have the 9/16" stud installed.
Full floater axle side note: The bearings in the hubs gets lubricated with the oil from the rear axle and not wheel bearing grease. When you assemble the rear hubs onto the axle coat everything with rear axle lube. Once you have finished the rear brakes and had filled the axle with oil. With the rear tires on the ground raise one wheel as high as you can go to allow the hub to fill with axle oil for about a half an hour. Then raise the other wheel. Then reservice the rear axle oil.
All of the brake lines I fabricated. The kits that I found out there are cheap. No one thought on anchoring the lines to prevent rub. It would just float around from master cylinder to the rear axle. I basically modify what the factory had for the single master cylinder for my dual master cylinder installation. I do have pictures if needed.