Identify a 70's road frameset I'm at a loss on the manufacturer of this frameset, any ideas are appreciated.

Its previous owner claims it is 50+ years old and was bought in Chicago 46 years ago.

Bike has Nervar Star crankset, Pivo bar and stem, and Simplex gear change. Also a French saddle. Frameset as shown with Campagnolo drops, wrap around stays, long point lugs, and flat crown.
My first clue was from the serial number which started with a J. The French derailleur also pointed me to this direction: I took a guess and searched for pictures of Jeunet frames.

Then, browsing a bit I saw this forum which shows many pictures of similar models where the lugs are exactly the same, similar dropouts and forks chromed. My guess; it is a Jeunet 620 or a very similar model.



Edit:

Well, I looked a bit more and found this catalogue. If you look at the course (racing) section, their top of the line model for that year is called 570-10 (10-speed 570). The marking on the dropout might be just that, the model number. Identifying the year, now, that's something else.