Many of those old generators where built in halves. Two six volts halves that combined to make 12 volts, it probably just has the one half, you can probably find a similar stator assembly that will bolt up that is 12 volts. I ran one for years on just one six volt half to keep the 12v battery from completely dying it only had a rectifyier, no regulator
and no lights, no nothing except power to the coils.
What is the diameter of the stator? I might have one that will fit, and the regulator, rectifiers to go with it.