Bumping with a quick observation - looking down the seat tube, there's no sign of a seam, and I can see where the butting for the 27.2mm seatpost ends, and the walls are obviously thinner past the butt. So odds are that this is a Tange 2 (or 1) tubeset. It should ride nicely - I'll build it up for my "beater" bike, but I've just been curious what model it originally was.