Ok, next idea. Getting a Cree in my KL1-R?

Recently I put together a KL1 w/ McR20 reflector which has to be the best reflector for LuxIIIs' out there! But of course, with everything going Creezy, I've just GOT to see if this is viable. I take it that I would have to drill out the reflector a little bigger. I see that the sandwich shoppe has McR20 for Crees' but are they different geometry or do they just have a bigger hole? Also, which of the Crees' would be better for the regular Mcr20 - the XR-E or the Seoul? I have a spare reflector in case I screw this up. Also I imagine I'm going to have to "mill out" a larger opening for the Cree to sit in, correct? Am I just blowing smoke? On 2 cells, I believe the KL1 pumps 500-550ma to the emitter. So what would I be looking at as far as output assuming this idea would work?