There are a lot of choices. It boils down to preference and money.
There are plenty of aftermarket "lamps" that you can simply drop-in (hence we call them "drop-ins") and switch to LED.
There are LEDs that are very inexpensive and produce a lot of light. However like anything else, price reflects quality.
For quality one name has stood above the rest and that is Malkoff. I would recommend getting a Malkoff M60. However Im not familari with the 660. I have a Surefire MP5 foregrip and it does not fit the Malkoff perfectly. It will work but there is a tiny gap between the head and the body.
Do you have a picture of your weaponlight? you mention "A42094" as a model, if I am correct, that is actualy the serial number.
Your 660 probably has a M2 style head.
http://www.surefire.com/660-Classic
This is designed for incandescent lamps. it has a shock absorbing feature to prevent incan bulbs from breaking. The downside to using this style head/bezel is that it does not do a very good job of heatsinking. LEDs do not like heat. So you want a head to help dissipate heat as much as possible.
If you want to swap in an LED lamp, then you need a simple Z44 bezel from Surefire.
http://www.opticsplanet.net/surefir...lens-type-iii-hard-anodized-for-c2-c3-fl.html
The other alternative is to simply buy an LED upgrade from surefire.
the BP60L is a weaponlight upgrade.
http://www.surefire.com/BP60L-LED-WeaponLight-Conversion-Kit
However it uses a P90L LED lamp which is now obsolete by Surefire standards.
Surefire now has a KX4 led head.
http://www.surefire.com/KX4-LED-Conversion-Head
Much better light output and an affordable price.
I hope that helps. if you have any more questions please ask.
