Check carefully - you may find that there are some differences in the boxes - perhaps in the way they mount to the frame member.

In any event, the best approach is to get your box rebuilt - new bearings and seals on the steering shaft are easy - and readily available from any bearing house as is the seal on the lower end of the pitman shaft. The hard part is the vertical bushing that the pitman shaft rides in. This bushing must be pushed out with a press and a new one installed. Then it must be reamed to the correct size by the machinist. Wear on this bushing is what usually kills the boxes.