Are there any articles or illistrations on how to adjust the power assist valve on a power steering gearbox?

All you can do to adjust it is to center it so it steers equally both ways. There isn't any adjustment to change the ammount of assist.

I probably explained it wrong, but I am trying to find out how to do what you just said. I'm looking for something with pictures to illustrate and describe what to do.

Loosen up the two bolts that hold the valve just so they are still a little snug. With the engine running and the front wheels off the ground gently tap the valve up or down until the steering wheel stays still and turns equally as easy both ways. What kind of problem are you having with it now?

Turns easy to the left and hard to the right. Tends to go left under acceleration.

Stumpys explaination is correct...just beware...a tiny adjustment (fore/aft) makes a huge difference, with the front wheels off the ground they can go slaming to one side really easy. As he said, leave the bolts a little snug, just enough so you can tap slight movement into the valve plate.