And how do I convert from 6vt positive ground to 12vt negative ground?
To go to 12v you'd need a later model 12v alternator.
To go to 12v you'd need a later model 12v alternator. Switching to negative just wire it with everything to negative ground and all your bulbs etc. to 12v. The stator for the alternator is a two wire one. Then get a Podtronics single phase rectifier for the alternator to charge the battery. You won't have a Magdyno on it if the motor is as late as you say, it's probably not a 61 year because they stopped using RE motors in 59' it must have a Magneto or Distributor on it. Easier to wire if you have a Mag. ERC