For the prime engagements in normal theaters (outside of RCMH) the distributor rented new plates and lenses. The image was 1.37 and was usually on the 1.85 screen (where I saw it, RKO Rt 4 Paramus, NJ, they opened the top masking to the 70mm height so it was larger than the 1.85 height) . If the...
When you get a chance, read the pages that Bob Furmanek has on his site about the 1953 changeover to widescreen production. Most of your questions are answered within.
Kubrick's last Academy ratio movie was Killer's Kiss. Everything after that one was theatrically presented in some form of widescreen. He liked Academy video transfers in the analog 4x3 TV era.