Owning a wooden boat for many years, I did a lot of painting; so I appreciate the comment about not wanting to paint. Gray AL won't reflect our summer heat here on the Gulf Coast as well as a white painted cabin; so hope you do a really good job of insulating the bulkheads and have some powerful ac. I am not sure what you expect to gain by replacing those FLs with any other engine - it seems like spending money you could use for other things on the boat. They are right sized for the size boat you have there. They are pretty simple and will run forever if maintained to any degree, and they are well supported, especially by American Diesel.
FROLIC (2005 MainShip 30 Pilot II)
Panama City area