Hey Mike
Do you still have the original bracket? Because you'll want a new one of them too, so you can lift the motor out of the water. As for the motor shaft - longer is better. 25 is ok, 30 would be better. you've got a relatively light boat with with the weight concetrated in the middle, and a flat bottom..she pitches with the wave action. If you want your prop and water intake to be in the water, get an extra long shaft.