Re: Mazda engine??
The good old KL 2.5 was a great engine, that was nearly indestructible, and with 170hp and a 7000 RPM red line was fun to drive.... In a car.
Even if you were to some how solve all the issues of adapting, cooling, and ignition protection, you are dealing with a short stroke screamer that really doesn't wake up till about 3000 RPM, and would want an outdrive with a gear set steeper than what exists.
Sell the engine to whom ever needs it for their 626/Probe/MX-6/Millenia, and use the cash to buy the correct engine for your boat.