Hey @Gordov2! Fellow C2 fan. I had a black one for awhile, ran it with a Malkoff M60 and two primary CR123's.
If you're ever tempted to bore out your C2 for 18650's, we've had at least one member have the experience of the light literally snapping in half. https://www.candlepowerforums.com/threads/broken-surefire-c2.483737/ The groove in the C2 where the rubber combat ring goes makes it very weak if bored. That being said, 16650's should work fine.