Getting your old drum off can sometimes be painstaking. Especially if your adjusters are frozen. After that, I would suggest pulling your axle shafts out and removing your hub. Unhook your brake hose, unhook your parking brake and then remove the 4 bolts holding the backing plate on. To re-install, do it in reverse.
If you go with the 14B drums, you'll have to upgrade to 9/16 studs. Not to mention there is a few different depths of drums out there. You'll have to find what works for you.
Here's a good article on the Eaton/14B brake swap. There are some differences in the Early vs. late Eaton hubs too. The later axles were slightly wider than the ones found in AD trucks.
http://67-72chevytrucks.com/vboard/showthread.php?t=536119Your best/easiest swap is to find a 12" brake setup from a 3600 truck.
