Thanks everyone for the great info.
She was pulled out of the water today at Mac Marine in Palm Beach. I purchased a long shaft 15 hp 2 stroke that I will mount on the starboard side of the transom. The shipwrights will giver her plenty of reinforcement. I'll only use the OB under low power, she is quite powerful for the boat and it is quite heavy. The OB is a long shaft, not an extra long, which I have been searching for since May without success.
My partner and I are new to sailing so we don't envision the motor being dunked by rough seas as we will be behind the heads in Pittwater but over the long term I will get the IB running and plan to try my hand at sailing in the blue water.