Worst case, buy a new 3 Watt Rayovac from wallyworld.
Yeah, I know, a big step down if you're a Surefire owner. I am, too, but it does as well as a G2, comes in an nice machined body, and takes AA batteries. You can drive it on 2500mah Nimhs to cut your costs. And I like the whiter light.
A drop in will probably do better than the old fashioned incandescent bulb in everything but focus/spread. The color will be different, but you'll get used to it, and the runtimes are so much better you'll be able to use it more without worrying about the dreaded dim out.
LED's are going to radically change lighting in America across the board. Cars, homes, and public areas are already seeing the death of the inefficient incandescent bulb. Edison's run of lighting is coming to a close.