Yep, as everyone said. Facing it is using a piloted cutter to get the edge perfectly square and finished. Has to be done to tap it. You don't even need to deburr it since facing it will recut the edge anyway. If your cutting/deburring is good, it'll only remove a fraction of an inch of metal. Tapping it is the expensive part. Needs a special tap/bit that your smith is going to have you pay for (lol). It's easy work. He may do it while you wait of he's not busy. Just takes tooling that's too expensive to buy if you don't do it for a living. Have him reset your bead for you, too. He'll most likely tack that on for another $10. Reset the bead even if you plan to use fiber sights later. Most fiber sights index on the bead. Only skip the bead if you plan to solder on a ramp etc.
I've cut down a few dozen singles in my life. Have quite a few around the house and shop here now. A cut down and choked single is my idea of a perfect turkey gun and it makes for some handy home defense, too. Fun guns.
Btw, welcome to the forum, S.O.! I knew I didn't recognize your face! lol
rich