Regarding which motor shaft to get will depend on how it sits out of the water. That is the determination. The one from Hunter takes a standard shaft but get the motor aafter you install the motor mount. In fact, take the boat with you when you go to purchase the motor to be sure if using anything else or better yet even with the bracket from Hunter.
Hunter use to build boats using for lack of terms plastic. Wood was encapsulated between the plastic layer and in the foam as aluminum is difficult to adhere to plastic. On the back of the foam was glass which was impregnated with Plexsis, not the standard hardener found on fiberglass boats. (Standard hardener found used on fiberglass, will destroy plastic)
The Hunter 15 is a fiberglass boat which has the aluminum backing plate encapsulated in the glass. If you are not sure, when drilling the hole, drill first with a small bit and see what comes out. If metal shavings, then it is aluminum and if wood, then wood.
crazy dave condon