Remember this is your steering. If you're not familiar with any of the terms or procedure it may be best to leave it as is.
From 87 rear drive manual:
"Sector Shaft Adjustment
(1) Disconnect center link from steering gear arm.
(2) Start engine and run at idle speed.
(3) Turn steering wheel gently from one stop to the other, counting the number of turns. Then turn the wheel back exactly half way, to the center position.
(4) Loosen sector shaft adjusting screw until backlash is evident in the steering gear arm. Feel the backlash by holding end of steering arm between thumb and forefinger with a light grip. Tighten adjusting screw until backlash just disappears.
Continue to tighten to 3/8 to 1/2 turn from this position and tighten locknut to 28ft.lbs. (38N.m) to maintain this setting."
It doesn't say, but I shut the motor off for step 4.
With all of that done you should not be able to feel the box come over center. If this is not the original box, you might do well to make sure the steering arm is on the box in the right position. It can go 4 ways and I've seen them on wrong. If you do this adjustment without the box centered it could jam as you try and turn the wheel. Not a good idea on the road, thus my warning, procede with caution.
BTW, I've done this adjustment on 2 cars and on C class motorhome. Worth the effort.