There really isn't any. That tiny 10 bolt rear axle has all the brake that will fit as it is. The only real upgrades would be expensive, some naturally, more expensive than others.
You could buy a kit to convert to rear disc brakes.
You could swap in 3/4 ton axles. Those are about the only things you can do. Both could set you back $1000 before it's all over.
I linked to Stainless Steel Brake Corp. through your web site. They do a big brake conversion for the front of '73-'87 Chevy/GM Trucks: 12" rotors, calipers, everthing you need for $549. I think that's a good deal. The rear disc conversion is $725, maybe that's a good deal too for what you get, but I think the fronts are more important. So I'll start there.
Hey Chuck - what about swapping out that six-stud 10-bolt for a 6-stud 14-bolt semi-floater from a 88 and newer LD 3/4 ton. It has a 4,800 lb capacity, 3" (me thinks) brakes and enough strength to handle 400 ft/lbs from the engine. I may be all wet here on the width of the housing, spring pad and shock mounts, but I may not.
Alternately, can the 88 and newer 6-stud axle shafts be swapped into place for the 8-stud axles used in that year of truck? (so the spring pads, shock mounts, etc are ok.)
Alternately again, like you said Chuck, is to swap to 8-stud axles, then I guarantee you will not stop at 33" tires.