Had the same bike (except the 22.5" size) in high school and college. The tubing decal said "LuxeTub", which I interpreted to mean seamless high tensile steel. Dropouts were forged and chromed.

What did you do with the Mafac Racer calipers? Was there something wrong with the original Mafac demi-hoods? Why not keep the SunTour alloy derailleur, which would've been a period-correct upgrade? Discerning folks want to know...