From experience I can tell you that if your going to start upgrading from 6 volt, then go all the way to 12 and enjoy the difference in cranking power, 12 volt battery availabilty, 12 volt regulator availability that doesnt have to be tampered with etc, etc. You can still keep original apperance of the starting and cranking system if done correct. IM me if you would like more info on how this works.
Thanks
Ken
