OK. I know this may sound stupid but how fast will the drum turn if you took the pulley off the motor shaft? There may be enough grab to turn the drum belt from the shaft alone but you should significantly slow the drum down. I'm guessing the pulley is about 3" in diameter and the shaft maybe 1/2" at most. If that works you can do something to the shaft to increase the grab of the belt. It's a hail mary but then again why not?