The aftermarket stuff is 95% C10. The C20 disc brake aftermarket stuff is so expensive it's not really worth it. My '65 has power drums and stops just fine. If you've got non-power, find yourself a booster and make sure everything's in good working order. That drum brake system is plenty good. The only way I'd bother with front discs is if I decided to use drop spindles and therefore required to convert.
If you really want disc brakes, you can do the front fairly cheaply by using later model truck parts like 73-87. That's a whole 'nother thread. Try doing some different keyword searches here and you'll probably find some info.
-David
