Z-Bar question regarding hole under clutch rod post

It looks like a way to lock the shifter in gear when leaving it parked on a hill and would release when the clutch pedal is pressed. I've not checked the '64-65 service manual. A z bar interlock is shown for valiant and barracuda other than 383 equipped in the '68 service manual. An external gear shift interlock is shown with a forward link toward the z bar.