dont get me wrong a regular street carb will work on the boat but a marine carb is designed specifically for boat use. Marine carbs have no ports to accomodate carbon boxes and things like that, marine carbs are different if you use a street carb you are jeapodizing the safety of the boat and its occupants.
I strongly suggest that you either buy a rebuild kit which is probly best if you know someone that can do a quality rebuild or drop the coin for a reman carb from a reputable marine dealer.