It's just easier to pull the box. It'll save you a lot of effort and time in the overall picture.
Disconnect the lines last and have a pan underneath to catch the oil. Other than that, just un-bolt the thing from the steering shaft and use a ball joint separator to pop the pitman arm off the center link. Good idea to replace the pitman arm too while you have the box off and since you have to pull the pitman arm anyways to do the seal. If you have the room and the arm isn't super stuck on the box, it may be easier to remove the arm while the box is still attached to the truck. If it's really tight, do it off the truck in a vise.
