Allan, there should be almost no play between the steering box input shaft and the universal joint. Getting the box adjusted correctly is more work than most are willing to put forth. Need to score the top allen screw to keep track of it. A very fine line to get all the lash out of the box and not set it too tight to accelerate wear and reduce returnability. Other thing you want to check is the pitman arm pinch bolt at the bottom of the box. You may be deceived into believing you have lash in the box when the reality is you are getting some incremental movement of the box splined output shaft without a change in position of the center tie rod (drag link). My guess is if your box feels good just off center than there is nothing wrong with it. These boxes are very robust. You simply need to draw the respective involutes of the worm and sector gears a bit closer together by adjusting the allen set screw on top of the box. The challenge is finding that elusive proper balance.
HTH,
George
90 735iL/149k