Take another look at the OH-6. Looks like both a 5 blade MR and a 4 blade TR on an OH-6 airframe. Look up "the quiet one" project from Viet Nam days and you will find that configuration, as well as sound deadoning for the engine area. I wonder if that serial number was one of those machines bailed to Air America during that project. The actual mission for that design was to execute a wire-tap with no-one knowing about it. Interesting reading.
Air America's Black Helicopter | Military Aviation | Air & Space Magazine
http://www.pprune.org/rotorheads/233...n-vietnam.html