Try unscrewing the sleeve that is around the steering shaft. It looks like the pinch bolt held that area tight so it should unscrew fairly easily, if it is in fact threaded. I think the up and down clearance on the worm gear is controlled by tightening/loosening that sleeve. After reassembling, you can remove the square head plug and temporarily install a grease zerk so you can pump chassis grease into the box. Normally they have a heavy gear oil in them but I have found the old seals leak but will not leak with chassis grease. The grease doesn't have any ill effect on steering.
By the way, I put a worm & sector box similar to yours (it was from a 30's era Chevy truck) in my International and found it to require lots of arm strength to steer, even with a large steering wheel. I then put a '40 Chev truck box in it and it too was hard to steer. It now has a recirculating ball Ross box in it and it requires little muscle to steer. However, you could be just fine with your set up.