Taking a longer look at the seat tube this morning, it's likely a 27.2. The side to side measure is 26.82 but front to back is 27.35. The cutout slot at the top of the seat tube is tapering slightly smaller toward the top. This may call for some gentle persuasion with a one inch hardwood dowel. I don't want to scratch that lovely paint job.

Not often my wife comments on the bikes in the lab, but she gave up an audible "wow" when passing by with the day's laundry...