While it had (theoretically) half the pulley friction, the Sport likely suffered from poor shifting, a problem that the dual-pulley derailleur fixed. It was rather quickly discontinued, and the hanging dual-pulley design introduced in 1960 lasted well into the 1980s before being replaced by more modern models.
The example of the Sport shown below (from Campy Only's collection) is unfortunately missing the pulley, but it's possible from the photos to get a good idea of how it would look when installed on a bike. Note that it's designed to fit a frame that does not have a derailleur hanger.
- Posted using BlogPress from my iPad