Many low production boats, in fact most boats, of that era did not have an owners manual. Some manufacturers would use a loose leaf binder (like you use in school) and insert instruction and parts information from some of the equipment that they installed. Most predominately things like the engine manual, head, bilge pump, oven, stove, refrigerator, etc. They might have put a few mimeographed pages, and a few usps handouts. But. it's rare to find an actual Owners Manual. I'm guessing very little of the equipment you now have is original. You can go on line and find a lot of information, as most of the equipment manufacturers are still around.
If there is something specific that you need, you can edit your question or go to a cite like Iboat.com's forum and ask. but you need to be specific and include photos and details.
I am looking for the plumbing and electrical schematics