I purchased this bike locally from a Goodwill in Colorado Springs, surprisingly enough. It was totally out of place to my eye, and I'm sure there is an interesting back story on how it got there, but I don't know the story. It was clearly a step up from my Viscount road bike that I was riding at the time. Even so, I simply hung it up in the garage to work on it later, not knowing that later might mean 30 years later. Somehow, life kept me distracted from that project.
The seat pillar looks to be 27.0 mm in diameter, according to my Omega pocket calipers. I can't find my digital calipers at the moment to get another reading. The seat post is fluted, so that may throw off my measurement a bit.
Thanks for the more detailed information about the bike from your practiced eye -- most impressive. It bugs me that one pedal end cap is missing, but maybe I can find one if I'm really patient (hopefully not 30 years patient).