Don, Just some suggestions. Drain the diesel
fuel tank, replace with new diesel. New
fuel filter. I have a '75, 27 ft hunter. The engine has never had any work done on it. Sucker just runs and runs. When it is running, you might look for any
exhaust leaks. I always keep the inlet valve closed when not on board, and check the cooling water outlet flow when I first start the engine. You could also replace the water
pump impeller. It will need replaced some time and now might be a good time for you to become familiar with the procedure. Oh, yea. Change the oil. You may have to draw the oil up out of the dip stick tube. My engine has not drain plug.
Good luck.
Phil in FL