Ok, just to set the record straight..
DO NOT ADJUST YOUR STEERING BOX! Very rarely is steering play ever in the steering box itself. That nut at the top adjusts the gear mesh inside the box. If you mess with it, you can cause yourself some very serious issues. They are set from the factory with approx. 4 in. lbs. of drag to them. If you increase or decrease the drag, the gears do not mesh correctly and you will find yourself not being able to steer. There have been several situations where someone adusted that top nut and then found themselves in an accident because the steering gears bound up and they couldn't turn.
I had this happen personally. I had play in my steering. I recieved some bad advise and "adjusted" my steering box. It made a slight improvement in the steering, but didn't correct it completely. Anyway, I left it "adjusted". About 3 weeks later, I was driving down the freeway at approx 75 mph. I was coming out of a long sweeping turn and I COULD NOT TURN MY STEERING WHEEL! I was in packed, fast moving traffic. I was headed for the other lane and lots of other cars at a very fast pace. I had the presence of mind to hit the flashers, hit the horn, and hit the brakes as fast as possible. Traffic scattered around me, and I made it to the shoulder of the road, but I could have killed someone and myself!
My problem was my wheel bearings on the drivers side. NOT the steering box.
You need to check everything else BEFORE you even consider the steering box. Check;
1. Rag joint
2. Drag link ends
3. Tie rod ends
4. Wheel bearings
5. Check for loose spring bolts (shackles and u-bolts)
Do a search on the subject of adjusting the steering box. This has been covered MANY times before. It is a VERY BAD IDEA.
Sorry to come off so strong, but I damn near killed myself and other innocent people on the road following bad advice. If your steering box has that much play in it, the gears inside are shot. It needs replaced. Period.