Delphi does make custom boxes for the Bronco vendors. They make parts for whoever is willing to buy them. Normally it is OEMs, but they will do it for anyone. It isn't a complete special steering box, it is an off the shelf 600 series design. Delphi custom makes them with different torsion rods (steering effort, amount of boost), ratio (they have a couple different ratios tooled up) input spline, and sector shaft spline. Boxes are drilled to spec as well. Delphi leased out one of our buildings at work many years ago. I knew a few of them back in the day.
The closest mix of junkyard parts will be a Nissan Xterra/Frontier box with a WJ sector shaft. I ran just an Xterra box as it has a larger sector shaft than the WJ/Bronco sized shaft. When you have issues with a steering box, often it is a bent sector shaft, so I kept the big one.