I think you can make a great light with the M3 as a host but there will be some significant design challanges! For starters, the shock isolated bezel works against you in terms of a good thermal path. If you plan to mate your LED somehow to the reflector which I assume is likely, the isolation will keep the heat building up in the reflector from good passage to the head. With a pedestal mounted LED, you can get the LED where you want it and you can provide a thermal path to battery tube and subsequently to the head via thermal paths designed behind the reflector and this might be sufficient.
- Don