WeaponLights are based around Housings - in the case of Housing Bodies (such as the A21 Classic Universal Housing Body, or the MH90 Millennium Universal Housing Body) the A19 extends rearwards between the housing and the TailCap whereas the A12 extends forwards between the housing and the Lamp Module.
Just to be clear - the A19 will attach to the rear of the MH90 Millennium Universal Housing Body used by the M96. It fits between the MH90 and the TailCap just like it would on a standard flashlight such as the 6P.
However, SureFire does not offer any Lamp Assemblies for the M96 with A19 (creating a four-SF123A body). You could replace the M96's Z46 "M3" bezel with a Millennium TurboHead (from the KT4 TurboHead Kit) and use the MN60/MN61 Lamp Assemblies on the four-SF123A body.
If you require the WeaponLight to be extended forward of the MH90 then you need an A12 (which fits between the MH90 Housing and the LU10 Lamp Module).
The Millennium Universal WeaponLight system uses standard TailCap threads so the standard Z41 LockOut TailCap will fit and function, as will a Z58 Clickie TailCap. The SW01, SW02 (Clickie), UMxx and XMxx TailCaps were designed for the MU WeaponLight system.
If the M96 you are interest in does not come with a remote tape pressure switch you can purchase an XM07 for it.
If you're considering an aftermarket cheap alternative - remember there is good reason they are cheap - they don't handle the current well at all (especially from three SF123As) and will heat up fast, perhaps even failing in short (sic) order. There seems to be a general trend away from tape switches on several of the forums I visit that concentrate on WeaponLights and weapon-mounted lights (ones that aren't SureFires).
This photo shows the MH90 hosting the U2 Bezel (it's actually a Lamp Module) and the U2 TailCap (like a Z58/Z59 but Black HA finish)
This photo shows the LU10 Lamp Module being hosted by the U2 body
Hopefully this shows what is the LU10 and what is the MH90.
Zach,
You ask whether the A19 can be used in place of the LU10 Lamp Module Housing Body.
No. No it can't.
What are you trying to achieve?
If you let us know there may be a solution I can work through for you...
Al