I can tell you that it's not a simple optic for reflector swap. I've installed an McR20 in an L1 and I ended up making my own heatsink and rreflector retaining ring for it.
I would do a search around. I have done this mod before, I think that is the correct reflector size. It was a direct swap for me on a KX1/2 head (E2L, E1L, E1B). I think it should be similar for the L1.