Look through the late 70's early 80's catalogues there and try to match up the components and decals. It's a little tough, because sometimes the French used one name for the bike in France and a different one in the US, and some with the same name even have different tubing depending on location. But yours with 531 and NR would be on the level of a US Super Corsa, or the French Olympic or upper Tour/Trophy de France.