I would add that if the Harrier neck is a "last fret overhang" in the style of Warmoth's 21 fret necks, you may not have to reposition the bridge as the distance between nut and bridge would be the same when either neck is attached to the body.
Of course if it isn't and the whole neck is longer than the Mighty Mite, you're going to have to reposition the bridge as recommended by the other BC'ers.