Your situation makes me think of all the people who replaced their Atomic 4''s with diesels, and the problems they had with the diesels not having as much torque as the older gas engine. This meant that instead of 6 knots with the gas, they got four with the diesel turning the same prop, simply because it couldn''t spin as fast. Perhaps newer diesels run at higher rpms and have more torque than before, but if not, this could be an expensive drag on your trip.
i want to clarify this statement.
diesels have MORE torque than gas.. torque is rotational force, not HP... for the same hp diesels have WAY more torque.
what has happened with these swap outs is that the rpm changes...
if you switch from an atomic 4 to a diesel, you will have to at the minimum have the prop re pitched.. maybe even an new different diameter prop...
a diesel inboard is the most reliable (other than electric) propulsion you can have. by their design they last longer.. they use a light oil for combustion. this in and of itself will help lubricate moving parts.
but i do agree that if your boat did not originally have an inboard... stick with the outboard.