My Embassies goes as follows: The '67 one is 37,5 (+ 0,00 something) mm at the nut. The '64 one is 38,0 mm at the nut. Now, the manufacturing years is something I'm not sure of. Those years are what I was told, when I bought them 10-15 years ago. None of them's got their serial number left, so I can't be sure about the age of them.
33 mm sure sounds a bit stripped down, Wymanised.