Wotan - You are correct, the main difference between the Chemineau derailleur and the French Cyclo was the indexing. The Cyclo, which dates back to the same era, used a continuous loop cable and moved the derailleur by means of a screw mechanism. The Chemineau has two springs, the door spring for chain tension, and an internal one to change the gears.

Stringbreaker - The front changer is actually quite common. It's an early Simplex model, and works very well with double chainrings, even if there is a large size difference.