Puch has sometimes nice frames, I've seen the 531 mark on several. I once had a 1960s Puck, old type 26" wheels, lugged steel frame, drum brake Sturmey AB hub, very typical bike for it's time. The frame and lugs were similar to your racer. Regarding the racer: gears, drives or crank sets often get repalced as the years go by, might have happened to this bike.