Cy,

On the valve cover of your engine, there should be a label that has the model, hp, spark plug etc. Also on that label is the wide open throttle operating range. Whatever prop you choose should put you in that range when you run W.O.T. You should try to get it on the high side of the range, which will allow you to put weight in the boat (passengers, fuel coolers etc.) and still remain in that range. If it falls below that range, you will tulip an exhaust valve. If it is above, over-revving damae will result.
Everyone is right in this forum, the only way you know for sure is to try the prop. This cannot be done over the phone. Anyone that gets it right on the phone made a good guess.
Good Luck....Hope that helped