i have a johnson 25 hp and i need a new prop it is worn out been looking for a little bit and found these two.(http://boatpropellers.iboats.com/Evinrude/25_HP_(1969-1977)_10.00-Pitch_Propellers/30/?rotation=Standard) the motor is a 1975 johnson 25 hp. my question is whats the difference in...