A couple questions that hopefully may lead to the truth:

Is 27.2 marked on the seat post?

Has the post and/or tube opening been measured with reasonably accurate calipers?

I'm leaning towards identifying is as a Super Course. The location of the serial number doesn't seem consistent with it being an International or Competition. As rhm states though, it could possibly be a Carlton, and measured seat post size seems the most telling clue we have available here.

Interesting bike, bigwoo. Eager to hear what you think of the ride qualities.