You need the seat tube OD (probably 28.0mm for a French bike) and the seat post OD (26.4mm in a 28.0mm tube would indicate butted tubing, probably 531). The brand of dropouts (Simplex?) would help, as well.
Based on the integral derailleur hanger and chromed stays, I am guessing this is a PX-10 equivalent. If I am right, this is a keeper, if it is your size (way to tall for me).
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069