I think it's pos ground, not 100% sure. A friend had an early flat fender and it was 6volt pos ground. When they look up what battery size it calls for where you buy it they should know for sure. My 46 Plymouth is pos ground. Make sure if you run a 6volt battery that you have 6volt cables. 6volt systems require bigger cables, bigger cables allow more current in to turn it over better. Everybody will try to get you to switch to 12volt but if everything is working like it should there is no need to.