I'm not real sure of the physical differeence in the heads for a 413 62 model heads. The compression varied depending on the motor. One was 13.5 and the other was 11. Does any of you know where one could see a pic of heads in question lying side by side, top and bottom so that i might become better educated before i start spending my money on something that isn't the real thing. Thanks for the help guys and gals.