Z-Bar question regarding hole under clutch rod post

I'm converting to 4 speed from a 903 auto in my '65 FS w/273. My Z-bar is the same as the one in this picture, it has a hole in the very bottom, below the stud for the clutch rod. The '65 parts book does not show the Z-bar hole, the service manual does, but it isn't connected to anything. The picture on Brewer's site for '64-'66 w/273, shows the same Z-Bar, so I believe it to be correct. What is that hole for?.

Z-Bar 2.jpg