The Gran Sport derailleur used a push/pull rod to move the cage left and right. Pulling on the cable forced the rod out of the housing, moving the cage to the right (and the chain onto the large ring). This arrangement worked OK, but would have been at its best with cranksets on which the chainrings were almost the same size. Later designs, which we still use today, move the cage diagonally outward and upward, better matching the differently sized chainrings on more modern bikes.
The Gran Sport was offered for some two decades. It became the Valentino in Catalogs #15 (1967), #16 (1969), and #17 (1973). By the time of the classic Catalog #18 (1984), this Gran Sport design had disappeared. The example from the CampyOnly collection shown in these photos reflects the longevity of this item--look closely in the bottom photo at the inner face of the outer cage, and you can see a wear pattern that must have taken years to develop.
-- Posted using BlogPress from my iPad