I was rebuilding a carb I bought from the junkyard (from an '86 Chevy truck) and decided to install the bushings just in case. However, based on the very limited play I found when I pulled out the shaft, it probably did not need the bushing kit.
The kit I bought from Cliff's performance came with 2 sets of bushings, so I'll probably eventually use it for my original '75 vintage Quadrajet.
I switched to the later model Quadrajet because it had the externally adjustable APT and some other improved features. It was also one of the last models they made before adding any electric controls, so it was an easy replacement for my old carb.