Hy sstock, unfortunately both six and twelve volt starters have the same number of teeth on their starter drives (if I am remembering correctly) the drives do have a different pitch from one another though, so they each fit the different number of flywheel teeth. If you friend is using a twelve volt starter the he needs the twelve volt flywheel with 168 teeth. There were some six volt solenoid type starters for cars, but I don't know how long a six volt solenoid being fed twelve volts all the time will last, the starter will be okay as long as the engine is not having to be cranked excessively to start. So you know which flywheel you have, now you have to determine what starter you are using and make adjustments so you have a compatible flywheel and starter, hope that helps.
