You can only adjust the steering box in the centre position. To do it as per factory it is done with a spring balance. You remove the pitman arm, fit a 8 and a qurter inch arm to the steering worm shaft and you then adjust to a resistance of 1 to 1,5 lb when pulling on the end of that arm.

Whatever you do don't try to adjust out play at anything other than straight ahead, you'll kill the box on short order because the wiorm has a high spot in the centre position.

In practice jack up the front wheels and adjust so there is no play straight ahead. The box should not go noticeably stiff there, personally I do it by feeling the actual steering column in the engine bay, the steerring wheel gives way to much leverage and you will over adjust.

regards