Do you know where to find a full manual/layout for our vehicle? Have you ever had to reconstruct any parts of your RV?
You might try eBay, doubtful if still in print. Or try to find a digital copy by googling.
Is this an RV built on a Ford E350 chassis?? And you want a manual for the RV portion? You will not find such a thing. They never did exist except in the files of the company that built it in the first place - which you don’t tell us. Ford didn’t build the RV part, they only built the van cut-away chassis it is built upon.
Your best bet is to tear it all out and start over with an RV this old. The interiors are not designed to last for 40 years. The wiring will start a fire if you don’t replace it all. The plumbing will leak. The tanks will leak. The valves won’t seal.
I am sure you didn’t want to read this but you’d be better off starting with a newer RV.
This is a site on CarTalk . You need to Google dedicated RV forums and call RV dealers near you. Not sure what you mean by ’ reconstruct ’ .