Unless you are looking for more exotic/racing or maybe cleaning capability on a 4wd --the oem rear drums brake fine and the parking brake is excellent as is.
Rebuilding the oem drums may entail drums, shoes, wheel cylinders, and harware. --probably all for under $100. Or there are those out there that did make the switch to rear disc. They probably have good drum parts to unload like I do.
http://67-72chevytrucks.com/vboard/s...d.php?t=178840