Addam...my comments were not directed at your 63, it clearly has hallmarks of a Carre-built frame, not just the willow leaf seat stay caps but also the fish-mouthed seat and chain stay ends at rear dropouts (assume same on fork?). Carre tended to use Prugnat S on his top customs which he modified with hand-cut windows but he typically used Prunat 62s on bikes he built for racers including those who were at the top of the heap in the 60s (TdF winners Anquetil, Aimar, and Janssen). Race bikes were a tool and Prugnat's top level S lugs were clearly not required to win races. Your 63 appears to be such a race bike, only thing missing are some racers initials stamped on the seat stay cap...again, really cool bike.