This is simply NOT rocket science.
Didn't your mothers ever teach you to do some research and homework, as well as comparison shopping? Really.
Heat exchangers: Good Guys at SENDURE & Heat Exchanger Source & Flix
Kubota equivalents: Universal 5432 & M40 engine information
in addition to the earlier posts which came from somebody who'd already FOUND the information on the internet.
Google is your friend. One design owners associations are invaluable, like this one: Diesel Engine - C34
How many of you still have M25 engines with the old alternator bracket that can fail catastrophically? Maine Sail and I and others have been writing about this issue for over 15 years.
You really do have to spend some quality time looking around, finding boats like yours with engines like yours. Our C34 website is pretty thorough, the C36 skippers are great, as are the Ericson skippers. We all share systems and engines and have already "found" most of the answers to the questions you are "whining" about.
Do some research and you'll find your answers, 'cuz most of it "is already out there."