531 tubing if used on the whole frame and fork, and Campy DO's will usually be a sign that it is a high line model on older Gitanes. It was on later 80's race bikes that they used Columbus tubing on their top line race replica models. The "72" on the head lug usually denotes the angle of the headstock on the frame. 72 degress is quite typical on C&V French bikes which gave them a lot of stability (IIRC, my 1984 Peugeot PSV has a "72" also stamped on its long point BCM head lugs visible under the paint.), but I had seen many Gitanes that had steeper geometries. Like the "Criterium" model that my brother had.....