You have a chrome bore 2.4L, so there's not a whole hell of a lot you can do to it to make more power before things start getting stupid expensive.
If it's running well and your compression is decent (120ish psi) it's healthy and if it's on the boat in your avitar, I'd leave it alone. The best upgrade you can do is a set of fiberglass reeds from Chris Carson Marine Service, and if you're in the mood for premium fuel or even mixing AV gas, mill the heads to get the compression up a bit. Chris Carson also sells reed spacers to stuff the crankcase a bit more now too.
What are your current speeds? How is the boat mainly used? What are your goals for the boat?