Which model Glen-Aire do I have?

Hi all, I'm trying to sort out the wiring going into the Glen-Aire furnace in a 1972 Shasta 1400. The only number I couls find on the furnace is L 420789, but I don't know if that's a model number or the serial number. I've Googled it, nothing specific comes up. A previous owner cut and spliced wires outside of the unit, added what looks like a relay, changed wire colors several times, and basically made a mess of things. It does have a thermostat mounted on the wall which looks like it's original to the trailer, but I'm trying to figure out if this thing runs on AC or DC (DC I think), which wire is positive, which one is negative, and what to clean and look for before I light it for the first time. Finding or downloading an owners operating manual or instructions would be great also. Don't know if this is gravity or blower operated, either. Anyone got any ideas?