That would appear to back the other valid NG documents released by the DOD. They are all in monospace font and some have the underlined and vertically aligned superscripted th which was available on some Selectrics.
I'd be surprised if the NG really used Selectrics. I was in an Army Reserve unit back then, and I'm pretty sure all our typrwriters were manuals. Selectrics were expensive, and usually involved IBM maintenance contracts. Pretty high end stuff for a Guard unit. But I suppose it's possible.