Saginaw 700- and 800-series steering boxes (bottom and middle) are strong, extremely plentiful, and cheap. Used in both cars and trucks for decades, the internal ratios can vary. While sector shafts are nearly all the same, the input shaft spline and diameter vary, so check before ordering your steering shaft U-joints. They can be found with both three-bolt (middle) and four-bolt (bottom) frame mounting points. They are interchangeable but four-bolt boxes are arguably better for strength.