In my experience, searching for the owner's/operator's manual for an old product isn't always successful until hitting upon the perfect set of search parameters. This was the case for me just last week in searching for the owner's manual for a 35 y.o. dehumidifier. It took several attempts, but I was ultimately able to match my unit with online photos, then onto a .pdf download of the manual.
So, in an effort to help out, if you provide the specific type of pump it is, along with the manufacturer & model number, and preferably a photo(s), maybe one of us will get lucky.
Curiously, has this pump been in service for the past 40 years, or has it been out of operation for a long period?
Anyway, if you would like some assistance in searching, I'm willing.