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YES! This gearbox can be adjusted, and its design isn't much different than what they used back in the 70's. The procedure for adjusting this requires removal of the gearbox from the truck, centering the stub shaft, and making the adjustment until it takes about 10-12 inch pounds of torque (using a torque wrench) to rotate the stub shaft.
Realistically, if you can get to the adjuster bolt (refer to the following illustration), you can try tightening it 1/4 of a turn at a time and driving it. If you get to the point to where the steering wheel doesn't want to center, or the steering gets too touchy, then you've gone a little bit too far and you'll need to back it off a little. If you leave it over adjusted, you'll experience premature failure of the gearbox.
Before messing with the gearbox adjustment though, you need to make sure you also check your ball joints
and control arm
bushings. Jack each wheel (one at a time) from under the lower control arm, as close to the wheel as possible. Push in and out at the top of the wheel, while observing for horizontal movement in the upper ball joint and control arm bushings.
Then use a prybar to pry upwards from underneath the tire, while observing the lower ball joint for any vertical movement. Any play at all in these components can cause wandering, noise, pulling, and irregular tire wear. You don't want to risk damaging your gear box until you're sure that is the problem!
#6 is the adjuster bolt, #5 is the adjuster lock-down nut.