Be careful with the open transom. My boat had twin Yam 150's and an additional 5" on the transom. Wasn't enough. I just spent a year rebuilding my '76 23 cc after it sunk because of the extra weight and the open transom. I glassed in the transom, added a bracket, and went to a single 250. The boat is faster, better fuel economy, and drafts 7" less at the stern. I have a lot of personal experience with the situation you are about to be in, be careful with the open transom!!!
