Is there something wrong with the existing box?
If this were me, I'd pull it off of the frame when the other steering parts are removed. Replace leaking seals, if any. Then perform the TWO adjustments per the service manual. Inspect the frame for cracks and rust. If the frame is OK...put the existing steering gear right back on.
Lots of steering gears get replaced when all they really need is an adjustment, and maybe some seals.
If this were me, I'd pull it off of the frame when the other steering parts are removed. Replace leaking seals, if any. Then perform the TWO adjustments per the service manual. Inspect the frame for cracks and rust. If the frame is OK...put the existing steering gear right back on.
Lots of steering gears get replaced when all they really need is an adjustment, and maybe some seals.