I'm thinking that it IS a Windsor: the fork crown is right and the fact that it has the 26.8mm seatpost, lack of chrome and added top-tube cable guides could be explained away as a a unique variation and/or a respray with some brazing done. Why the owner wouldn't have sprung for more braze-ons is another question. But Windsor seems to have had more in their range in their offerings than just the Pro with its chrome lugs and other Cinelli details, and the clunkier looking Carrera with its crude (and chromed!) lugwork. It's a weird one, but I'm becoming convinced it's a Windsor...and since i don't know the specific model (Windsor owners don't seem to have a fanatic registry like Cinelli owners have, imagine that!) I'm dubbing this "Mexinelli", I like the ring of that. Thanks to all who responded!