You shouldn't have to use any glue if you got a good set of Mac overlays. I found the glue on the Macs to be more than adequate. Not only that, but in order to peel off the old faces, you'll have to unscrew some tiny hold-down screws. These screws also aid in keeping the faces down on the plates. Just remember to clean the face plates as best as you can to ensure the new faces lay on smoothly without any rippling.
I hope you got the Mac's and not those crummy overlays that you just cover over the stock faces. Those suck a$$ and peel/bubble like the wind.
