I have a 1980 Masi GC made in USA, marked MC53 on the BB shell. The length of the seat tube is 53 cm from the point on the top of the seat lug to the center of the BB. It measures 52 cm from top of the TT to the BB center, and a little under 51 cm center of seat lug to center of BB. At a local vintage group meeting there were three other ‘70s GCs marked to smaller sizes. BTW, it’s too small for me if I set up with the standard Campy 2-bolt, Brooks Pro or Concor, and 10 cm Cinelli or Nitto Pearl stem. It IS a great ride, however, despite the very steep seat tube.
Which measure is the size you are looking for?