The second motor I would suggest is the 1928 or 1929 Elto Speedster. Even though you spin the flywheel (in the opposite direction you want it to run) to start them, these aren’t considered a “Row Boat” motor by some as they are not brass. Although rated at 7hp. its closer to 11 or 12. They have a very interesting ignition that will need some repair, and the coil will need to be rebuilt as the wires will be rotten if you find an example that has been resting for decades. The gas tank is the biggest issue with these because of the vibration. Look for cracks around the mounts. They will all have dents. If they will let you, pour in some alcohol and check for leaks. I’d show you how to get the alcohol back out but too many links here and everything disappears. They don’t use an impeller but there are no seals in the gear case so it needs some regular attention if your running them a lot. Your son may not want this much of a challenge but all the issues were over come. https://youtu.be/lJ6cXeWWi7g
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.