How many hours on the engine? Are you the original owner or do you at least know the history of the boat?
If it was running fine before and everything else checks out, perhaps a really light hone job on the cylinder bores and new set of rings and put it back together. I wouldn't touch much else.
Do the crank journals and con rod bearing shells look OK?
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, Acme 1285, PPass, rear 750 sacs, KGB, IBS
(previous) 2001 X5, 1991 TriStar 190