Several things to check.
Is the differential centered on the frame? Measure from the outside of the frame to the inside of the wheel on both sides. They should be pretty close. If not you need an adjustable track bar. Start there.
If that's OK, then center the wheels by driving straight ahead when you park. Remove the drag link from the pitman arm. Center the steering box by turning the wheel to lock in one direction, count the number of turns it takes to turn to full lock in the other direction, then turn back half that number of turns. Now look at the position of the pitman arm. It should be pointing to the rear of the Bronco, and anywhere from parallel to the frame to pointing slightly to the drivers side.
At this point, does the drag link fit back into the pitman arm? No? Then adjust the length of the drag link, or get an adjustable drag link.
There's a couple other things to look at. Maybe before disconnecting the drag link... Put the front differential up on jack stands so you can turn the wheels easier. Turn full lock in each direction. See if the stops on the knuckles hit the differential on either side.