Follow the advice of John above, but once you have tightened it down as he explains, turn the steering wheel (with the front end up off the floor) and see if it gets tighter and stiffer near the extreme left and right ends of the turn. If so, you'll have to slack off on the adjusting nut that you just tightened down. You don't want to be turning a corner and have the steering wedge over there and find you can't steer it back straight. Loosening this back means that it will have more slop as you are driving on a straight road.
To correct this, buy a kit with a spring-loaded peg that fixes this problem from Herman Van den Akker (
https://www.hvdaconversions.com/) or from Ken Gillanders at BFE (
https://www.britishframeandengine.com/parts.html/). Both are in California.
I had this problem and bought a kit in 1992 from England and it has fixed the problem. I've driven about 85,000 miles since putting the kit into the steering box. All you do is take off the old top cover (3 bolts) and after putting in a new gasket and the new top cover, bolt it down and adjust it as per the instructions.
If you think about it, 99% of your steering is done with small corrections on roads that are almost straight. This causes the conical part that engages in the slot of the worm to wear. Or the worm sidewalls will wear. Not all over, only where all these small corrections have been made.
The kit is designed so that the peg is spring-loaded. With the spring, the spring holds the peg down nicely near the center where the wear is - and when you steer to the far left or right, the spring permits the peg to move upwards so it doesn't wedge or get tighter.
Here is a photo from a friend in Holland who had this problem and one of the peg kit on my steering box. No judge in a concours can see it because it's behind the air deflector. Your driving safety is more important that an originality point.