If you're getting it from the junkyard, try to get the aluminum spacer that goes between the box and the frame. They often break, so it's a good idea to have a good one in case yours is bad. There are aftermarket upgrades available too (sorry, don't know links but I've seen references here). If you can get the bolts from the donor, grab them too so you're ready in case you shear one off.
When you put it back, make sure you get the steering shaft and input shaft of the box mated before you bolt it up, since you can't replace the shaft with the box in place. They could have designed this so that when you loosen the top clamp it would slide up the column a quarter inch more, but they didn't, so it won't. If you have someone else to help here it can be useful, just because you'll be upside-down on the ground holding the box, and it's a bit heavy.