If the issues you mention are all that's wrong, you're doing well. There is nothing wrong with six-volt systems on these trucks, unlike some others like big cube GMCs and I-Hs. Unless you want to add 12V accessories, it would be just fine to get a good quality six volt battery and troubleshoot from there. Unless you have automotive electrical experience, the details of a 12V conversion will drive you to distraction. With a 12V battery, and a 6V generator to charge it, the battery might have gone dead soon enough so as not to damage the gauges. It would have burned out the light bulbs in short order though. Do they work? If they're 6V and OK then the rest of the system probably is too. I say probably. Maybe nobody turned on the lights since the 12 V battery was put in. Maybe it was dead when they put it in, in which case you lucked out all around.
