Congratulation on the new acquisition. Having owned, several older coaches, there are some things I learned. Figure out who made the chassis, Ford, Chevy, etc... From that information, you can search for information on that chassis for the running parts of the coach. Any nearby parts store can likely help if you give them the model and chassis number from the chassis.
Coach parts are mostly standard across the industry. Take the generator for example if it is a 3000W Onan, you can search for the Onan model number followed by manual to find information about the generator. Luckily on the older units the controls are simple, unlike the newer units. Perhaps no more than one small panel with a volt meter and a start button.
Another resource is the Tiffin factory. They still have some old folks there that remember how the old units were assembled so a call to them may net you a manual or other help.
As for where the batteries were located, you can start tracing wires and looking in compartments, in cabinets, under beds, etc. There will be big cables from the generator to the battery location for starting, just as there are big cables from the engine to the engine batteries. That is one place to start. It is possible that there was only on set of batteries instead of two like the newer units have. My first rig only had one set of batteries. If you left the lights on at night you could not crank in the morning.
It is likely that all the lights and other equipment inside runs on 12 volts as some of then did not have inverters. This place has lots of useful parts
https://www.etrailer.com/maindept-RVandCamper.aspx
I hope you find what you need. Fixing up the older units is a lot of fun and very rewarding.