I'm doing a bracket install and looking at motors too. I have a standard fully closed floatation bracket with 30" setback going on a 21' reinell pilothouse. I've only been looking at 25" shaft motors. Now I am questioning the possibility of a 20" length so the float bracket will sit lower on the transom. This should provide more displacement and reduce any tendency of porpoising. I guess the argument is that the motor could be swamped. Any thoughts?