various internally regulated 12V alternators can be modified for 6V - I had one on my '46 and it was great, totally eliminated any cranking problem even in the coldest weather, kudos to my local auto electric shop - and our friend Fifth Ave has been
selling them for years all it takes to use an internally regulated 6V alternator is to take the wires off the old regulator and jump 2 of them together - but can't remember which at the moment - someone here will recall, it's been discussed
Bill