Another 50 centimeter sized bicycle for your consideration.
This Alex Singer is from the mid 1970s. During the busy “bike boom” years Cycles Alex Singer had some frames made by CNC in Paris, including this one. It was built up in the Singer shop using nice components like Maxi-Car hubs and Spécialités TA cranks. The bike is in used-not-abused condition, as found. It measures 50 cm with a 52 cm top tube (both center to center).
Lots of photos in the Flickr set
Alex Singer 1970s, a set on Flickr.