The easiest way to tell is by looking at the round brace rod which attaches to the middle back side of the moldboard.
HS = grooved end with corresponding washer - also is slotted for adjustment
NU= flat end with hole and bolt through it only...no grooves
Parts are available for both kinds (I have them among other plow parts).
As Carlyle stated, it's most likely HS bottoms,but I've owned several with NU bottoms (made after 1968). See the link below for more information and pictures.
Tyler in IL