As a few others have said a 10 HP would probably be all you want on that boat. Large outboards put excessive pressure on the transom.

Tip #1) If buying new, get a 4 stroke. If buying used, look around UNTIL you find a 4 stroke. You'll thank me later. I have a 25 HP 4 stroke tiller steer on mine and I can talk in a near normal volume back and forth to a passenger in the front of the boat as I'm running near WOT up the river and idling it's super quiet. You'll have to yell loudly back and forth with a 2 stroke. That noise gets old quick.

Tip #2) If you buy used, make sure it's pissing good even at idle.

Tip #3) Pull the lower unit oil plug and make sure it's not metallic looking oil.

Tip #4) If the prop is in rough shape on the motor you get, go ahead and invest in a new one. It's a good time to match the pitch to your needs also. You can find a good deal online. I have a brand new 9" aluminum prop I'd give you if if will match whatever you end up buying. You only have to promise to carry that boy fishing often to claim it. You can buy a hub kit for it for nearly nothing. I don't remember the pitch though. I think it's either a 9 or 11 pitch.

Tip#5) Listen to Hevishot.