Sgt Slaughter – A (Un)Real American Hero?

The combination of Sgt. Slaughter being the break out star of your 1981 Mid Atlantic rants and my renewed interest in GI Joe – thanks to the brilliant piece of nostalgia The Toys That Made Us, on Netflix – got me to thinking:

Is there any concrete proof or reliable sources that Robert Remus actually was a US Marine, let alone a Drill Instructor? The internet seems to believe he was. The timeline is a bit off too, at least if we are to believe that he was a DI.

If he wasn't a US Marine DI… is this the greatest pro wrestling work of all time? 

​Time Magazine seems to think that he was a legit drill instructor.  More importantly, ​Wikipedia reveals that he went to high school and played football in Eden Prairie, MN.  This kind of blew my mind, since I just finished watching the third season of Fargo and it's kind of cool to see one of the (storyline) locations of the show revealed to be a real town with real people that came from there!  
Also, if you've never watched Fargo, it's on Netflix, and it's GREAT.  Just sayin'.