RE: New boater looking for some advice
You may think I'm crazy, but I would try it without the gearbox. That bigger motor looks like it's too much for that gearbox. You would only need to reverse the rotation of the motor and make some motor mounts. As for your spin-out problem, try a turn fin . You need to make sure the fin is at 90* to the bottom of the boat and not parallel to the boat's side