That looks like an entry-level mid-'70s French frame to me, equivalent to a Peugeot UO-8, approximately. Frame weight of 0.5 pounds heavier than a 531 frame sounds possible for straight-gauge tubing. French bike manufacturers didn't use stamped dropouts or one-piece cranks of the kind seen on U.S.-made low-end Huffys and the like. That doesn't mean it wasn't a decent bike for its time, but bike companies didn't do so many gradations of quality in those days.
The fork crown race looks suspiciously askew: front-end impact/bent fork/frame? You might want to check the top and down tubes near the head tube for evidence of damage, too.
Last edited by Trakhak; 09-19-11 at 05:51 AM.