Hi Chainmaker,
Once the vintage manual clutch is setup correctly it works really well, and has advantages over the automatic vintage clutch. You can slip the manual clutch when pulling hills or dis-enguage when you want to coast. The vintage automatic unit has one-way "dogs" and won't dis-enguage when you want to coast.
The vintage auto clutch units are around but normally cost over $400.00.
The best belt to use is the AX26, however some brands are shorter[Dayco ,Gates, & NAPA].
Have fun,