Interesting find.
I've not seen a WeaponLight without a "Z32" Shock Isolated Bezel, so it's either really, really old, or due to the etched logo, a special bezel put on there.
Anyway, it's not a "660". Well not exactly.
Ignoring the non-Z32 bezel, it starts with an L60 Lamp Module which includes the Lamp Module Housing Body.
Next is an A21 Universal Housing Body.
Then there is the TailCap switch.
In Classic WeaponLights the A21 was supplied with the TailCap switch.
The TailCap switch is a UxxT or UxxS
Where xx is the length of the remote tape pressure switch cable in whole inches. My guess here would be 04 or 05 inches.
T is for a constant-on flag switch
S is for a disable flag switch
Your description isn't specific but based on what you've written I'd guess it was a "T" constant-on flag switch.
The 1" diameter ring mount looks like the M10 Low Base Weaver (Female) light mount.
Attached to is looks like an M14 Rifle Barrel Weaver (Male) mount.
The 660 has the L60, U04 and the M10/M14 combination.
So since this has a flag switch, it could be a 660T.
If the cable is 5" rather than 4" then it's not a 660.
It's a 650-05T with M10/M14 barrel mount.