I'm leaning toward a non-French coachbuilder. Italy and UK have been ruled out, so I'm thinking Swiss. Because I think this car looks exceptionally modern for its date, I'm going to try a lesser known builder, who, my reference states, was "One of the most creative coachbuilders of the post-war period." So my complete puzzle answer is: 1953 Citroen 15CV coupe by Beutler.