There's just so many weird incongruities with the bike. Another is the 27" wheels for a top of the line bike. Even if it were a 73, I'd expect a set of 700c and I'd definitely expect them on a 80s model.

The Tange 2 switch seems to line up with what you're saying as Kactus' 1983 Sekai 4000 (http://www.bikeforums.net/classic-vi...ai-4000-a.html) is made with Tange 2 tubing.

So maybe this is closer to a 80s model than 73. But then where did that professional decal come from assuming the paint is original?