Southwestern vehicles are great! As I thought about my answer a little further, I realized that you can't get the gear box out without removing the Pittman, anyway - it wouldn't be able to come out through the frame...
Anyway, going back together - I always just get the steering gear box centered in it's travel (I actually make a cardboard pointer and tape it to the steering wheel end of the shaft), and count total revolutions to extreme travel in each direction until it hits the stop - divide by two, and turn back that many turns to center. (in other words, if the whole assembly will rotate 6 turns by watching the pointer, then go back 3 turns from the stop on either side). Now it's centered. Then, mark the steering wheel shaft for where centered is, a line drawn across the meeting point of that shaft and the top of the box (because it will move while you're working) - and with the drag link installed, wheels straight - that will determine where the Pittman has to be on the sector gear, it will only go on in one place.