You have several choices in steering boxes, and the first is whether you want power or not. If you're modifying the Jeep enough to justify a steering conversion, you'll want power steering. A Saginaw box from a Jeep will bolt up easily and won't require a special pitman arm. However, the most common source for suitable Saginaw boxes is GM cars. The one you want will have an input shaft with an 0.80-inch-diameter input shaft (most common on '60s and early-'70s cars). You will also want a power-steering box with four attaching bolts, not three, for strength.