The “it’ll make everything short and fat” didn’t seem right. I thought that, at worst, it would be pre-cropped for widescreen format, after expansion. Anyway, to check it out, I came across these Widescreen Museum: SuperScope pages with some interesting tid-bits.

Superscope was conceived and developed by Irving and Joseph Tushinsky. Their process was created in the laboratory rather than the camera. It was their contention that Superscope anamorphic prints could be generated from straight 35mm negatives, or from double frame (VistaVision) or other wide area negatives.
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Photography in the Superscope process was generally no different than normal non-widescreen films.
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While the first few 3 strip Technicolor films were released by RKO, all color product up until 1946 was produced by the independents like Walt Disney, Merian C. Cooper and Jock Whitney.
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Superscope was used in nine RKO Technicolor productions from 1955 thru 1957, and a few re-releases of older films including a bastardized conversion of Walt Disney’s Fantasia which featured the original optical Fantasound system adapted to four track magnetic stereo.
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Of course by now you know that no movie was ever photographed IN Superscope. Instead they may have been photographed FOR Superscope.