I bought this Marinoni off of Kijiji. The bike was listed as a 52cm, a perfect size for my one of my grand daughters. I did not even question the bike's size until a bit later...
When I got the bike home, something did not jive. The lady who owned the bike was the same approximate height as I am. With that in mind, I straddled the bike? Got off and snapped up the measuring tape. Not a 52, but a 56cm machine. No good for my grand daughter but perfect for you know who. Yup, me and the Marinoni is now my daily rider, when I can actually ride (been off the bike for a couple of months now with worn out hands that cannot pull a brake lever).
I got fooled by the over sized tubing which make the head tube appear to be short and proper for a 52cm size. I was wrong but still tend to look at head tube to approximate a vintage road bicycle's size.