For 25 bucks you lucked out! You can part it out on eBay and easily more than triple your money.
So what you basically have is the guts(L60 body + A21 extender) of the "Surefire 660 Tactical Light" commonly referred to as the "Black Hawk Down" tactical or weapon light, WITH some upgrades (the newer style M2 bezel and XM0x tailcap) as stated above. You said you have the Weaver 1" ring mount (correctly identified above as the "Surefire M10" mount) which would attach to the "Surefire M14" barrel mount.
Originally, it would have been issued/sold like this, attached to the bottom of the M16 barrel:
Later sold with upgrades:
Also, they had these (this is one of a couple that I own):
M2(older style) bezel +
L90 Body + A21 Extender + XM0x tail switch + M10 weaver ring mount
(this has the
P90 incandescent bulb and takes
three batteries)
The tactical weapon light were usually sold in the "lego" style I think because it was convenient to have them modular and interchangeable among different Surefire weapon lights. For instance, you can take the head/bezel + L60 body without the talcap and extender and attach it to a Surefire branded weaponlight handguardd (HK MP4, Remington 870, Mossberg, etc.) Same thing with the L90 body and bezel that I have.