find yourself a older good clean 9.9 have a dealer go over it and check it.
i fixed mine myself cost me $100 all together now i have it on my 14ft IM SO HAPPY I DID!!! if your worried about the 6 cyl. so much why dont you rebuild it since u got the boat for free? just a thought. check into dealer used 9.9 longshaft you can get a hell of a deal.