Rating?

There was no MPAA in 1963.

"Have you ever had... an Egyptian Feast?"

the old ratings board probably gave it a M for matured audiences, or might have refused a rating at all!

I was 14 when this was released to theaters.

I was an avid horror fan and always checked the 'movie listings' in my newspaper every day.

I actually cut out the ad for this (along with 2000 Maniacs) because it took up at least 1/3 of the (normal size) newspaper the day this opened here.

It had the text 'for adults only' (of course which saddened me) and it was only shown at a drive-in. My guess, and I didn't go, was that since teenagers were the prime customers at drive-ins that no one was turned away.
The irony of it all, is that 25 years later, I moved in with a friend that lived a couple hundred yards from this drive-in. The screen was visible to at least 50 houses surrounding it. Just have to wonder how many unsuspecting residents wandered out into their backyards and saw this groundbreaking gore-fest.

As mentioned earlier, no MPAA at the time. It was up to each theater to decide who could or could not enter. I still believe that this drive-in made no effort to keep anyone out.