If you have a "breakback" trailer you'll want a short-shaft motor. They're great in that you don't have to get the trailer wheels wet when launching but the boat does go in at a steeper angle than the "float-off" type and there would be a risk of scraping the skeg on the slip.
Mine had a Mariner 5 2-stroke when I got it and the previous owner had modified the mount to get it to fit. It's critical that the leg goes down the hole without touching at the front and that the back of the motor doesn't rub on the back of the well. When I changed to a Mercury 5 4-stroke I had to make another new mount! I've also got a "sail" prop with big Mickey-Mouse ear blades which pushes well. Snags are that it catches weed and ropes etc and you can't easily get it up and down through the hole with the prop on - a disadvantage if you race to the published yardstick.
Geoff Harwood Cygnus P21/30