Didn't we do this go-round a year or so ago? I'll repeat for consideration the Pathfinder - still in business, I believe, based on the world-wide ubiquitous VW Rabbit diesel. I'd think that the engine parts would be available as easily as any of the others world wide.. the marinization parts (pumps, manifold, etc ) are mainstream brands like Jabsco, Perkins, etc. Aluminum block for reduced weight and the last time I checked they were pretty favourable on the price point. Turbo versions are now producing over 60 HP I believe and based on the larger 1900cc engine, but I'd probably avoid a turbo for various reasons.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)