Heat exchangers are not usually brand specific, and a manufacturer like SEN-DURE, INC. | Manufacturers of Heat Exchangers and Oil Coolers
probably made the one on your gen set. If not I'm willing to bet they have one on the shelf that would be a good replacement.
Exhaust elbows can be fabricated by any good exhaust shop. The original equipment ones are usually substandard anyway and they do have a lifespan.
This information might be helpful for you, or for whoever helps you take it out of the boat.
Still can't get over Dockside closing