As I expected, you guys supplied some great info (some of it conflicting, but never mind...).
I checked the frame and it has a serial number starting with M and ending with 62. Could it really be a 1962? I'll have to look at the info again, but I thought they didn't get started till the 70s.
Also, sadly, the decals specify Tange Champion #2 , not #1. I feel less of a man. But I guess that just means I have to start looking out for a 5000 with that super-light tubeset.
The reason I asked about the possibility of being designed for 27" wheels is that I need long-reach brakes to hit the rims. (Remember I bought this as a frameset, it came brake-naked.) Currently have some LR Tektros on there but switching to some long-reach Paul Racer centerpulls. I measured the reach at 57 mm.
Again, thanks for all the info. Hope to meet some of you in Austin at the NAHBS if a time and place gets set up. My brother and I aren't bringing our bikes but we're renting some townie bikes to get around on.