Looking at the Surefire G2 LED light I dissasembled it and the incandescent Pentagon light.
The reflectors look similar but the surefire LED reflector is just a little shorter.
I installed the surefire reflector in the Pentagon head anyway since they both have springs in the reflector bases.
Once the Pentagon head is tightened the surefire reflector lights up and what a huge difference in brightness.
I am going to see if I can come up with a small fiber shim/gasket to take up a very small amount of difference between the two different reflectors.
So, yes, it looks like there is a way to convert the Pentagon incandescent head to a LED.