The "overrun clutch"sloped area.....that mates to the overrun clutch slope on the rear of F gear is on the correct end of the prop shaft. The other end has vertical walls to mate with the vertical walls on the rear of the R gear because there is no "overrun clutch" function on R gear.....wasn't needed. Purpose of the overrun clutch is to allow you to come off plane (for example) by cutting your engine RPMs while your prop is disconnected from F gear and rotates at the speed the oncoming water spins it which will be faster than the proportional engine RPMs......keeps your teeth out of the windshield when you decelerate....if you had a windshield.
