I think the inner diameter of the airhorn is different... The key is what kind of carbs the 75F has. Are they like a 75K carbs? If so, then I believe you're okay. The K carbs from K0 through K6 have the same intake outer diameter and therefore the same airhorns. The PD carbs are different (larger outer diameter on the intake side of carb) and use a larger diameter airhorn.