Bob,
What other engines did you come across while you were looking that you did't consider worth mentioning? My engine search was very interesting. Had a good time looking. Some people like things decided and some like to keep things open. I'm in the latter group. This tendency applies to all we do.
I'm not sure I fully understand what you are asking. and I sure don't want to offend anyone by identifying their favorite engine as unsuitable for this application. But this kind of sums up why I choose this Cummins: I am not hung up on labels. Right now I have diesel engines in cars, truck, tractors and boats with Cummins, Ford/Iveco, Yanmar, IH, VW, VM, Volvo, MB and Iseki. My current Ford/Iveco marine engine runs fine, but I do not have enough confidence in it for a trip from the SF Bay to Alaska. So based on broad product support and parts availability in the West and PNW, and opinions from many from this thread, I had a lot of good choices. Cummins for me was on top.
I grew up in a Richfield Station (Atlantic on the right coast) and have been bending wrenches and fabricating most my life. Was part of a Super Stock drag team in the 70's and worked for Hooker Headers in the 70' and 80's starting in the Deign Shop. Today in retirement, as a hobby I have a full shop where I do my own hotrod/car restoration projects and work on my vehicles, tractors and boats. I am a DIY person. Deciding on the 6B for the boat was probably the same reason why most project hotrods are built with Small Block Chevys. They are common, most all mechanics know them, can get parts anywhere that I am going, there are many forums dedicated to them, and sensible upgrades and modifications are well documented. And like a small block Chevy in a hotrod, there is nothing I can't buy or fabricate for the 6B to make it suit the boat. I have had boats most of my life, but I am still relatively new to bigger diesel boats. This engine seemed to be the simplest, basic, no brainer to start with. I will be there when the old engine comes out and when the new one goes in. I will have the boatyard set and align the engine and trans, but I plan to plumb and wire it.
Again, thanks to all for helping me get to this point. I look forward to your responses to questions as I'm working through the repower.
Bob