1971 Dart Swinger Worm Gear Adjustment

Pretty sure that's a 5/8 nut.
Center the wheels, loosen the nut and work the steering shaft back and forth by hand while you lightly tighten the adjuster screw just until it stops moving easily.
Any more than that and you could end up with a bind up in the center.
This may need to be done again after you get it all tightened back up and turn the steering lock to lock.
The slotted screw should turn really easy, so not a ton of worry about getting to it.
You should be able to even turn it using a nickel or other coin.
Be sure to hold it while you tighten the lock nut again.

3-4 inches is a lot to try to adjust out and have a useable box, but maybe.
Start there and see what happens.