Very nice find, indeed. Too bad about the rust. I am first to encourage keeping original paint on a bike, but in this case, I'd opt for a re-paint. The rust seem very crusty around the TT cable guide. I'd fear for the frames integrity before much longer. Fortunately, the frame is rather spasely decorated. A good digital shot of the relatively simple headtube decal could be used to replicate it. French 531's are easy enough to come by. I'm not sure about the downtube decal remains, but they are too far gone to distingush, and that scratched in PITARD just HAS to go!
I'm sure someone like Norris Lockley could recomend a good enamalist, who could also do the boxlining this frame has and would need in a re-do. Only my humble opion.
New Britain, CT