No date stamp, but specs would indicate 1957-58. "Aerojet-like application of bright Harmometal on front and top and back edges gives brilliant contrast to the highly polished, rich-black finish" according to their 1957 catalog. They touted their design as "at the forefront of modern guitar styling." I concur. You, too?

There were several variations and body sizes of the H956. This is the larger "Grand Auditorium" size of 16 5/8" lower bout. Nut is right up next to 1-¾", and has a large but not overly chunky feel, which is typical of higher end Harmony guitars of the time. Bone nut. Ebonized fingerboard bound in celluloid. 20 fret neck (another later evolution) and 25" scale length. 

Top is solid arched (not carved) spruce. Back and sides are standard Harmony birch. Neck is "hardwood". Dunno.

Price in 1957 was a whopping $62.50 

This example is 100% original, very playable with low action and no fret wear