Now I used to work in a machine shop and when we had to tap a hole in a free standing structure we would use a hand drill to power it in as well as to properly align it. As long as you are holding the drill with the tap in the same plane as when you drilled the hole, the tap will align properly. After starting the threads with the drill, I used a cresent wrench to finish tapping the threads. Make sure to use a good cutting oil and to back out the tap and clean the threads frequently as it only takes 1 rogue chip to strip your threads or even break off the tap in the hole.
:EDIT: Hadn't thought about it because it didn't happen to me. When tapping this hole, take your time and check the depth. I got a PM informing me that they had tapped too deep and the fitting was bottoming on the sector shaft. Quick fix if it happens is cut a couple of threads off the fitting, debur the threads, and throw it back in.