I managed to shim the v-belt pulley and jerry-rig a motor mount, so I mounted up the little motor onto my Piaggio Boxer scooter, put the v-belt on, strapped the batteries on with duct tape, and shorted the throttle wires, and it ran!
The speed was horrendous, maybe 6 mph on a slight downhill and 3-4 mph on a level surface. But that's fine for the purpose of my test run.