My 40hp 4 stroke 3 cycle Mercury Shift assembly

[tomthumb]

I understand that Mercury has improved the shift shaft and cam follower assembly. I was replacing my shift shaft assy and noted that it would free spin and not turn left or right a few notches as it had been. I removed the gear housing and thought I had lost my cam shift but when looking at the parts list, it shows obsolete. I am confused as to how the cam follower shifts without this cam shift in place. What makes the motor shift into forward or reverse without this cam shift inserted in the cam follower.