I don't know weather or not these motors will handle it, but a 6v bulb will generally handle over 12v for a short period of time. Running higher voltage (within a reasonable range) will not short out a bulb, it will just make it really bright, and burn out sooner. My Packard still runs 6v, and the voltage regulator lets out between 6.12 and say around 7. Usually 6v generators put out around 8v depending on RPMs, and my headlights that are ran directly off the battery (fused of coarse) work fine at 8 volts. A 12 system charges at 14.7, and take, for example, a test light that uses an 1157 12v bulb; it does not burn out when testing if an alternator is putting out.
On a side note, 6v systems demand a MUCH HIGHER amperage. A 6v headlamp usually runs at least 30A, and some use up to 50A. Something with that kind of draw would almost definitely kill the motor. Perhaps you should try something that uses a 6v maglight bulb? Im pretty sure those don't use much amperage....
Anyhow, let me know what you discover. I've been wondering if the gens on these things put out ok or not. Good luck, man!!
