Here is the procedure that GM Saginaw Division recommends to adjust the steering box.
Disconnect the pitman arm from the sector shaft, completely back off the sector shaft adjusting screw on the sector shaft cover.
Center steering on the "high point" then attach an inch lb torque wrench to the steering wheel shaft, the torque required to keep the shaft moving for one complete turn should be 1/2 - 2 in lbs.
If the torque is not within these limits, loosen the thrust bearing locknut or tighten valve sleeve adjuster plug to bring the preload within limits.
Tighten the thrust bearing locknut and recheck preload.
Slowly rotate the steering shaft several times, then center the steering on high point.
Now, turn the sector shaft adjusting screw until a steering shaft torque of 3 - 6 in lbs more is required to move the worm through the center point.
Tighten the sector shaft locknut to 35 ft lbs and recheck the sector mesh adjustment.
Total steering gear preload should be 14 in lbs or less.
Install the pitman arm and replace back in vehicle.
NOTE: To try and adjust the sector shaft screw without doing the preceding will DAMAGE the steering gear.
Most of the play is not in the sector shaft adjustment, it is the spool valve area.
Here is a link to an article on the off-roadweb website on the Saginaw steering box with photos of the disassembled steering box.