Frank Berto reports that:
However there are various bits and pieces of evidence pointing to Excel manufacturing cheap, relatively nasty derivatives of European derailleurs (Simplex Prestige and Huret Allvit rear, Campagnolo Valentino front) in the mid-1970’s. These may possibly have been original equipment on Sears and Huffy bikes around that time.
Excel also manufactured the Elgin American for Sears.
In April 1974, Beatrice Foods, of Elgin, Illinois, filed US patent # 3,903,751, relating to derailleur design. The Excel Dynamic (and Dynamic II) derailleurs in this collection are covered by this patent.