Re: will any Surefire XM0 series of pressure switches work on a 6P body?
The U505B is a Type II Black (like the standard 6P) tail-cap/tape-switch for the Classic Universal Weaponlights (like the 660). It has 3 cables coming out the back, two that go to a constant on/off rocker switch. The 3rd cable goes to a momentary pressure switch. The rocker switch can be attached via the included velcro kit, while the pressure switch can be attached via a groove found in most modern fore-grips, or it can also be attached via the included velcro as well (great for older weapons with-out modern picatinny rail systems).
Due to these having the same finish as the 6P, these will probably look the best. The UMxx's are Type-III (HA) Natural/OD, and are designed for the Millenium Weaponlights (MH90 Bodys), although they both will work on either or.
It's pictured here on the top left of the picture (the U505B will fit on any of the bodies/adapters pictured here)
Get with CPF Member "flip" over in the Market Place...he usually has a good bit of weapon-light parts, and recently had a U505B that didn't sell, if you're interested.