I would have guessed about 63 at the least along the seat tube. I can usually guess now within a couple of centimeters on crappy CL pics. The 50-54 range is a little hard to judge. The kicker is that head tube length isn't always the clue visually. The 71 Super Course had a 56-58 looking head tube, but was 60 along the seat tube. I have noticeed sloping top tube bikes seem to run smaller these days, as if they're measuring differently. A 56 in a modern bike fits me almost perfectly, yet a horizontal top tube bike I run a 60-61. Must be the fact that almost everything uses a riser stem now(IE:no angle, but straight off of the steerer).,,,,BD