I just bought an '08 20XRD w/ Merc 250XS, it has the Sportmaster lower w 1.62 gears. The prop on it is a 27TXP and it has a Hydro Dynamics jackplate, not sure if it is a 12 or 14, it measures 13 1/2". Where would be a good starting point for the prop shaft hieght, it appears to be 1" below pad. Thanks....