Since the steering adjustment is similar, I’ll go thru a quick layman’s version…but, you will of course eventually need to overhaul the gear, as the bushings are most likely worn out, at the least. There are two adjustments, the worm bearing tension, and the gear mesh adjustment. First, jack up the truck so the front wheels are off the ground, so the steering is free to turn. Put jack stands under the frame!
The worm bearings are adjusted by loosening the big lock nut, then turning the bearing housing. On the 59 and older trucks, this adjustment is at the bottom of the box, at the front. On the 60-newer trucks, look at the top of the box, where the steering shaft (to the steering wheel) sticks out. Usually a hammer and blunt punch will loosen the locknut. The bearings should be adjusted to get a few inch-pounds of drag on the worm gear (steering wheel), but you can adjust it by tightening up to remove the play, then go just a smidgen tighter..and tigthen the locknut securely.
Then, adjust the gear mesh, which is a slotted screw with a 5/8″ hex locknut. Get the steering centered (wheels straight ahead), and loosen the locknut. Gradually tighten the adjusting screw in, while frequently checking the steering play by turning the steering wheel back and forth a turn or two…but leave it centered when adjusting. Eventually, you will take up the slack, unless the gears/bushings are really worn, in which case the adjusting screw will go all the way into the box! (not good). Tighten till the slack is all gone, then add about a half turn of preload to it. If all is well, you should feel the steering get just a little bit harder as you pass thru the center of the steering wheel’s travel. Tighten the locknut securely, and enjoy the “new” feel of driving your truck.
Also, when you finally get around to rebuilding the gear, you will want to have the shop manual for reference, so you can accurately adjust it. A few years ago I bought a few tubes of steering gear lube online…The correct GM part # for steering box lubrication is 1052182–Redline makes this exact lube which you can buy here on Amazon. This lube is neat, it’s half way between grease and oil. Oil is too thin and leaks out, but grease is too thick and won’t properly lube the re-circulating balls. Use the right stuff!