will this light work mounted in the 12 o'clock position in front of the fsp?

thanks..

If you have the handgun version it should work as well as the TLR-1 or X300 in same configuration.

What is the difference between the handgun version and the long gun version?

The difference is the backplate. The long gun version has a button in the rear or a lever, depending on version, to activate the light. The handgun version has the tilting switch like the X300 or TLR-1.

Long Gun version:

Thanks Yoda...

There is another "Long Gun" version with a non-pressure type selector switch.  I have both variants and the primary difference is the one pictured (which is part of the SOPMOD Block II Kit) can be activated either by pressure switch, pushing the large button, or by turning the selector knob to "on".  The other non-SOPMOD version (also referred to as long-gun) does not have that large button and requires the use of a pressure switch for momentary on/off.