I'm with
jonwkng,
Get two SF Z41 tailcaps, remove the boots, but leave the guts in. Bond them together, back to back. Alternatively get an adaptor made that's similar to the Z41's (Martin D White on CPF does this sort of thing).
You can now join any two hosts together that use SF tail threads. Surefire, Malkoff, Solarforce come to mind. Use a short P60 host at the back with a Red Solarfoce drop in, and the Lumen Monster of your choice at the front. Switch on and off with tails or heads.
I'd do Malkoff Hound Dog front with Makoff MD1 Body (Martin White again) and MD2 Head at the back. To early to think about drop ins.
P