I've watched both versions of LATT side by side, and there's really only a couple shots unique to the Academy version. (The titles and one shot of a handwritten note, IIRC.)
Things are being cropped as the animation drawn for Cinemascope was reshot with 1:37 in mind, but it's skillfully done and not obvious unless you've seen the widescreen version. It's weird that the Academy version has only ever been released on Laserdisc. Making a brand new pan and scan of the Cinemascope for DVD makes no sense.
Some screencaps showing the differences here.
http://animatedviews.com/2006/lady-and-the-tramp-50th-anniversary-platinum-edition/