The good news is you don't have to find Mity Lite information. The appliances are all name brands, that
sold to all the RV manufacturers. Just look up each individual item by the model number and brand.
The molded FG manufacturers made the frames, cabinets, and
fiberglass parts, at most. The rest all came from suppliers. Many didn't even make that much.
Lil Snoozy bought their shells from one supplier, bought their frames from a second supplier, and so on.
The great news to this is the brand may be long gone decades ago, but the appliance makers are still out there.
I would have someone test any
propane system over 30 years old before using it, and if the bottle is original, it is way past its certification date (so it will have to be replaced).