There are plenty of 12v generators out there. No need to convert a 6v genny to a 12v genny.

By 1956, everybody had switched to 12v but most didn't switch to alternators until 1965.

Find a 12v generator from just about any other car or truck between those years and I'm sure you'll be fine. Probably won't even be too hard to find one that fits the original brackets.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)