I am all for using nontraditional things and land based things in a boat, but this makes no sense. It’s OK to have a non-marinized diesel. Where you could put the radiator outside or something.
But to have a completely air cooled diesel inside a boat is just not going to work
. Noisy, hot, difficult to cool. Not some thing you want on your boat. Maybe if it was an open deck
boat. Even then, you need some soundproofing