It's later than '73 because it doesn't have the lame foil decals. If it's really 531, it can't be lower than an Interclub. I haven't seen that seat tube decal before. Could the rings pantograph on the fork mean Olympic?

Don't let the dropouts throw you. My TdF came from the factory with Simplex rear and Campy front. They made lots of substitutions.

Have you tried Gitane USA? You may get help from a real expert. You may also get lots of advice from someone with no clue. It's just like here.