Nocturne is not supported well for 10.8 and does not work well with fullscreen mode. The inverted overlay flickers and glitches a lot at random, the method i'm using allows a native inverted menubar and is pretty safe, and yes i'm on a 2011 27" iMac.
I am on 10.8. But, yes i agree there is an inverted glitch for full screen apps, which can get a bit annoying. But, again haha there are days when i want a black bar, but without damaging something original so i kinda stuck it out with this one.
You should post on how to do your method once you find a bit of time, perhaps i will give it a shot to see were i land.