Whiskey,
Your picture really caught my eye. It looks like a PROD or ECAS configured with a 4 blade Marine Corps rotor head. I went to one of my key reference sites (http://tri.army.mil/LC/CS/csa/aahist2.htm#AH1S) and found the following information:
AH-1Q anti-armor version (1973) was the result of the Improved Cobra Armament Program (ICAP), to fill the operational gap left by the failure of the AH-56A Cheyenne program. The AH-1Q had an M28A1E1 turret, XM65 TOW/Cobra missile subsystem, infrared sight, and XM128 helmet sight subsystem (HSS). The AH-1Q was equipped to fire eight Hughes BGM-71 130mm TOW (Tube-Launched, Optically Tracked, Wire Command-Link Guided) anti-tank missiles mounted in a pair of two-round pods on the outboard pylons. M200 19-tube 2.75 inch rocket launchers could be carried on the inboard pylons. The AH-1Q was deployed to Vietnam in 1973, but was unable to carry a full weapon load in that environment, leading to development of the AH-1S Cobra. The AH-1Q was the first Cobra to feature the snub-nosed Telescopic Sight Unit (TSU).
YAH-1R prototype was the result of the Improved Cobra Agility and Maneuverability Program (ICAM), essentially an AH-1G with an upgrade to a T53-l-703 1800 SHP engine, transmission and tail rotor, but without the TOW missile system. A second prototype, the YAH-1S, was a AH-1Q upgrade with full TOW capability.
For additional information and some excellent pictures of the AH-1S Cobra, go to Butch Lottman's AH-1S Cobra page and AH-1S MOD Cobra photos page. Also check http://www.midwaysailor.com/photos/cobra.html for some AH-1F(MC) pics. I found 1 pic of the YAH-1s at http://twdesigns.org/hueyhelicopters/history%20gallery/249.jpg.
Cheers,
Wade