After well over a year of procrastination I finally ran down to the social security office and made my McG name change official. I think that I was procrastinating because I envisioned long lines and indifferent staff --- something like the scene at your average NJ DMV office.
However the process was quick and painless. I was in and out of there in 15 mins (or maybe even less).
So I'm legally a McG now!