My brother in law has had a 350-400HP version on his JC 31, probably 4 years old. Its a charter boat and put away hard and wet. I've run it several times and been docked next to him for about three years. The engine runs even though some times its not perfect. This year he seems to be getting into replacing components like wire harness's, fuel lines and other things. He has had a real problem getting such parts, I know wire harness still wasn't available and fuel lines took him down for a week.
I will say be very wary of buying anything but standard. We bought a H&H 40 with a Mack E9, great engine in one sense, the E7 is SOLID. The E9 only 13 engines were marinized. I remember when we called and asked for a exhaust manifold and they said this is the last one... GULP. Not that Iveco is going anywhere but parts man, hard to get.