When, in the mid 1970’s Shimano redesigned its entire middle range of derailleurs, including the Shimano 500, Schwinn had the opportunity to move the Schwinn GT400 Le Tour on a generation to this - the Schwinn GT420 Le Tour. In doing so slightly more steel crept into the design - in the front knuckle.
I think that this was the last model that Shimano produced that was branded as Schwinn - from here on in, Shimano was a brand that was desirable in its own right. Today, of course, Shimano rules the world and Schwinn is viewed as a quaint piece of what Americans call history.
A tidy, competent derailleur.