Journey;
Sailboat transoms are not constructed like the power boats (thicker transoms) as many incorporate heavier and higher horsepower as those hulls are plaining hulls which require getting the hull up and out of the water to go. As for sailboats, they are displacement hulls and can only plow thru the water. Nearly every sailboat design is not as thick to carry large outboards to include the H 23; thus the thickness of the transoms are thinner. Even with a 9.9, the bow of the boat will raise up thus plowing thru the water slowing it down. Therefore, sailboat transoms are designed for 10 hp only.
Since I am familiar with that transom of the 23, you have a heavier motor. Look inside the rear locker storage area to see if the previous owner did anything to distribute the weight of that motor for example a large piece of wood, metal plate or metal straps which will greatly help to distribute the load on the transom vs. 4 bolts. I am not sure if you are still using the old motor bracket as well which needs inspection. Just remember not to use full throttle and teach others that as well if motoring for you. If you recognize the facts and adjust accordingly, you should be fine.
There are no stupid questions and if there were, boy I sure asked them long before you ever did. It is better to ask and be informed. There are a lot of folks with boats like yours and this is a valuable source or wealth of information to get from. You may even make some friendships and boy that is oh so true. Kermit is a good example as I enjoy that friendship along with Jim Seamans, Peggy Hall and many others on this forum. Welcome aboard sir and if you have a question, simply ask and we on the forum will be glad to help you.
crazy dave (only if you knew how I got that name)