If you want is 12volt for lights you can just replace the secondary coils on the Puch stator for a 12volt coil https://www.treatland.tv/puch-12-volt-light-coil-2-0-improved-version-p/puch-light-coil.htm
I did it on a maxi awhile back and it worked. You will also need a voltage regulator, those are cheap also.