The L1, A2 and now L2 tail caps are all the same and interchangeable among these three lights. They will NOT fit on any other battery tube. The L2 has its converters (2 of them) inside the battery compartment. If you can find a "smart" head that might make contacts when screwed onto the L2 you will have two different converters trying to run the LED. I suggest that a three legged potato sack race with two people who hate eachother's guts might be more efficient. /ubbthreads/images/graemlins/icon15.gif
The L2's head is a "dumb" head and aside from running it on the L2, the only other host that would make any sense would be to DD it on an E2(e) where you will have a low and cool running beam of light; dependent on the Vf of the specific LED.