We used to get a little 5 hp (evenrude I think-its still in the garage tucked away behind a boat) on the back of our 4m alongside the 50hp Yamaha without any real problem and without any bracket, just sat on the transome and scratched the cowling of the main engine when it felt like it !
The A frame was built spec for the boat and the previous owner by his friend in the s/s business (now there was a friend to have !)and took up no transom space at all. We did try it on a spring ebb (10m tide here ) once and had an onboard discussion as to whether we were actually moving and if so in which direction!