I have a SolarForce L2P with a XP-G drop in. It works with 1 18650 or 2 CR123s. I got an extension tube so I can use two 18650's for lt nit trail walks (longer runtime). Just make sure whatever drop-in you choose can take the range of voltage.
It's probably one of the best P60-style lights out there. Good machining and good anodizing.