One LED bezel I know fits for certain on a SureFire M3 body is the SureFire KL2. It has 19 white LEDs in it, and they're at least somewhat regulated. It runs for about 1.5 hours in full regulation, then falls off like it got its head slammed in the toilet seat.
Here's the battery discharge analysis chart of the KL2 I did in late summer 2002: