I am just getting into my very first experience working with any sort of armor whatsoever, and because of my freakishly massive melon-head I couldn't fit inside my bucket I elected to use the "face-off" method. Believe me when I say it was extremely tedious to cut the facemask off, but I used a dozen rare-earth magnets to hold it in place. Here's where I put them:

Not that I recommend it, but I can hold it by the cheeks and even swing it (slightly) and it's solid.

Here's the bucket from the sides--most people tend to cut in front of the "ears", but I went around behind. I got the idea from
Torment, and I really, really like it. The cut is almost invisible:


Here's the cut:

I'd MUCH rather work this way than trying to grind material off the inside of the cheeks, but that may be just because I still don't play well with Bondo if I grind off too much!