The sticker on mine was long since gone when I got the boat but I doubt if it was rated for anything over a 6-8 hp. And since they were built before the 4 strokes came along, they didn't consider that weight addition. With nothing more than the 2 little pieces of wood on either side, the transom can't be very strong. You might be able to beef the transom up a bit with some square tubing under the top lip of the transom that goes from one side to the other, and installing a full width piece of wood on the inside (or outside if thickness becomes an issue). Mine only had a little ½" thick small rectangle piece of wood on the inside and the same keystone shaped piece yours has on the outside.