Since I was a projectionist back then I can tell you for certain that no ONE matted aspect ratio was standard. Many theaters used 1:66 because a wider crop cut off heads on some films. If the theater ran old stuff this would be a real problem and remember, old Bowry Boys titles and Three Stooges shorts were shown widely.The mangement also like the flat and scope films to look drastically different since they were then touting scope as something special. And some shows went the opposite way.There was some pressure to mask at 2:1 for flat films and crop the sides of scope films so every film looked the same, thus no masking changes. Obviously that didn't succeed but I often attended a theater that did just that. And when they ran a pre-50's "revival" it was murder. And in the sticks a few shows were still using 1:33 and didn't have scope at all. So most films of the 50's were released full frame and masked at the projector. That way anybody could show it. I don't believe I ever screened a hard-matted print until the mid or late 60's.