Offer me a good price on mine and I will replace it with a 260HP Cummins/Mercruiser/VW TDI that is lighter than a 350 chevy in a heartbeat. Or a small home equity loan...
From what I learned working for a boat builder- it is all in the props. A 300HP 350CID engine doesn't make 300HP unless you can absorb full torque at that operating point. And prop efficiency can be from the 40s to 74% (or worse). So a 60% efficent 200HP drive goes as fast or faster than a 300HP 40% efficent prop. Engine power is input, not propulsive power.
A $600 prop and magic bottom paint could be the ticket with that engine.
Volvo IPS props are SO thin, you would think they couldn't be fully machined from NiBrAl (Bronze) on a horizontal CNC machine. But they are. And at thousands each, they still seem to be worth it. They are transmission and tires all at the same time.