When looking at the head tube pic above, I noticed two things I hadn't seen before. One is a head badge rivet, right in the middle below the decal. I just had another look at the head tube, and I can't find another one. Or two, which was kind of what I was hoping to find.
Also, it looks in the picture like there just might be a serial number under that paint on the lower HT lug. Just checked that again as well, but even with a torch and my strongest pair of reading glasses I don't see anything.