I'm posting a photo of the measurement-- why "guess..." ??? Do you think that I'm just sticking it on 25 to keep some kind of silly internet cred?

You're being thrown by the relaxed geometry of the frame. I love the geometry, it's what I grew up riding. Great for regular distance/pleasure/charity/commuter/century rides. It's not even a butted or chromoly frame, really only one step up from gaspipe, but it's pretty and shaped right. Who cares about an extra pound of steel in the frame when you're 60 like my dad and just toodling around or maybe riding to work on a spring Friday?

Anyway, c-t of the ST is the standard frame measurement that folks use, especially on an old frame. Like my 66cm Panasonic or my 62cm Jamis. The bike is hanging up from its rear wheel in my workshop. Too many bikes around to keep them all horizontal. c-t is what you see here.

I'm not going to get into an argument over what frame size fits whom, though TT length is most important to me. But it's still a 25". And I'm big. So's pops. Bike geometry's a complicated thing from what I gather.

Not sure whether I can still post about the frame in here, since I'm setting up a wheel build at the LBS with a SA 5 speed, with drops and a bar end. It should fit in the 120 MM rear spacing. (or should I post a pic to prove the spacing...?)