You could try a regulator from Cycle Electric before converting to 12v. They sell a square one CE-101 that would mount where the regulator does now on the stock bracket (hole pattern may be different) or the one that fits on the end of the generator CE-546. They are in Englewood, OH. V-twin doesn't carry all their products but a lot of small bike shops do. I think they come with a 2 yr. warranty. Wouldn't be stock but neither would the 12v conversion.
Bob Rice #6738
He that conquereth his own soul is greater than he who taketh a city.