Depending on year, the 233s and 255s were either Ford 351 blocks or Chev 350s. Both Fords and Chevs had Rochester carbs, 2-bbl or 4-bbl depending on horsepower.
The Ford-based 233s had an adapter to mount the Rochester 2-bbl but a Holley 2300 will bolt on to the Ford manifold directly. You can add a spacer for the PCV hose connection and you will need new flame arrestors. Carb linkages are pretty straightforward but will require some bracket fabrication.
Holley markets 2 marine
versions of the 2300, one jetted for the Ford 302 and one "universal." Hit their website and do some comparisons, they also have a "remanufactured" department with lower prices. Summit Racing
has a good collection of adapters and spacers and fuel line connectors.
Some interpretations of USCG Regs for gasoline power require solid or shielded fuel lines and double hose clamps on hose barbs, and flexible fuel line has to meet A-1 specifications. Fire-shield on the hose may satisfy this requirement.
on both carbs will almost certainly be cheaper than switching. If you operate the boat so that the secondaries never open, and they have become corroded closed, you have turned the 4-bbls into 2-bbls anyway. If they run well the way you operate them, might want to wait for the rebuilds until you sell the boat.