welcome to the garage zombie, 12V started with the 55 2nd [for Chevy] - there's nothing wrong with 6V as long as it's well maintained - it's also easy, and "visually correct" to convert to 12 .... the 6V wiring is heavier than that used for 12V, so it'd work fine, just need to add a couple things to prevent frying things like gas gauge, heater fan and radio
look around the electrical forum, it's well discussed from various viewpoints ... also see the tech tips section, where you'll find step by step on it
Bill