Decent cubes with modest HP is the way to go for reliability, When I built my 383 I went way overboard on the internal using a full Lunati Pro mod kit over 5K in the engine stuffed in an 010 block with Dart IE heads I put a mild Lunati roller cam and got a modest HP engine with very nice tractability. Sure I could have gotten 75mph like some others but 65 is just fine plus 4 MPG, the engine runs through a Bravo Diesel X notice I do not like things that break. A few have said why spend that much not to go as fast as it could have, to me a dumb question my goal was a near indestructible engine and boat both of which are very over built for what I ask them to do.
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.