I own a 1981 Marine Trader 41
There is no manual for your boat. There may be individual manuals for the motor and all the systems. You should make up your own boat manual.
To do this you would, in one place make a list of all your systems. For example
1) Engine - manual eg FL120 or Perkins etc
oil/ fuel filter change history
2) Electrical - Batteries
3)Domestic Water system - Pump
You get the idea. You should have a table of contents book so you can find the various manuals you have. A trawler is nothing more than a collection of systems. By organizing these systems in a dynamic library, that you can update as you do maintenance, you will have a on going record of your boat.