OK, let me be more specific about the Seasall engine.
Some years ago, Cummins and Mercury formed a partnership to sell the VW based common rail engines. They were similar to the Seasall: high rpm, high power. A few were sold in the US.
But there was no dealer support. The Cummins dealers didn't want to invest in understanding that engine, because they didn't like it. The Mercury gasser guys had no clue. Eventually the partnership was dissolved and Mercury now tries to sell those engines alone, but I don't know of any builder that installs them.
Now look at the Yanmar/BMW marine engines. When they came out, they were the cat's meow: light, low noise, good fuel economy. But the marinization was for ****: no water cooled exhaust manifold or turbo. Yanmar, who has a good dealer network and should know how to do stuff right, stepped up to the plate, recalled all of the engines, installed a water cooled manifold and a heat shield for the turbo. That got them back in the running.5
These three manufacturers: Yanmar, Cummins and Mercury know a thing or two about the US marine engine business, and they screwed it up. Seasall/Hundai know nothing. Can they make it in this market????
The Seasall does not have a water cooled turbo. I don't know about the exhaust manifold. I do know about the US dealer network, nada.
If you want to cruise at 18 kts with that boat, you will need to produce about 200 hp which was the wot speed of the old Camano with the 200 hp Volvo. 200 hp is 67 hp per liter for that engine. That is off all of the charts for continuous, long term use.
I would install the JD in that boat if I was willing to go slow, 10 kts or less. If I wanted to cruise in the high teens I would look for some more displacement either in the Cummins or Volvo line.
If you are willing to go slow and not stress the engine, then the Seasall might be ok at 120 hp or less as the upper limit for decent engine life is 40 hp per liter. Then you could sell your boat someday to some unsuspecting clod who thinks that 270 hp will take him to the upper teens.
But you will be blazing a new trail with that engine with no dealer support. Good luck.
David