I changed out my manual drums to manual disc. I probably upgrade to Power disc in the future, but for now I really see no need to. Manual disc work fine. You don't have to change your pedal either. Several companies make Powerboosters that work with your manual pedal using an adjustable rod. Transam racing is one. That will probably be the one I go with when I decided to go w/Power Disc.
"When the chips are down, the buffalo is empty"
Brett C. MCA#51647-'68 FB w/289, T-5, Dark Highland Green, 3.40 8"