At the bottom of the steering box,you'll find a forged bracket that is attached to the steering box,and it has 2 bolts that hold it to the box.This bracket also supports the advance & retard/hand throttle tubes.
The bolt you need to loosen is the lower one,where the machined split is at the lower end of the steering box.Once the bolt is loosened,turn the large plug with the 4 slots in it,to the right to remove any excess endplay in the steering gear main shaft.Then re-tighten the clamping bolt.Just make sure you don't over tighten the slotted plug adjusting nut,tighten just enough to remove any endplay.
This information can be found in the Chevrolet Repair Manual for Chevrolet Capitol & National Cars,Series AA-AB,on page 116(my copy anyway).You should be able to get a copy one from the Filling Station or other sources.Hope this info helps you out.
