Originally, it was a (+) ground, 6 Volt system.
MOST 12 Volt conversions are (-) ground, but some guys kept 'em (+) ground after conversion.
Polarize generator BEFORE startup to whichever polarity you decide to go with.
MAY 12 Volt conversions retain the 6 Volt starter, in typical use, there's no harm to the electrical parts of the starter, but they DO engage with more of a "snap" on 12 Volts, and that can sometimes shorten starter drive life.
Some guys have suggested using a long run (looped out of the way) of light-gauge battery cable to help soften starter engagement a bit.