Originally Posted by
unworthy1
those clues point toward "Japan": the 26.8 seatpost could indicate Tange tubing (possibly Ishiwata), that nut on the downtube for shifter means either SunTour (was there a Shimano "aero" shifter that used this?) and seen on a few Miyatas (and sister Univegas) and Nishikis.
I concur, it looks like a fairly high-end Japanese production frame from early to mid 1980s. The fork crown is an Ishiwata SCM:
Are there any ribs inside the steer tube? Five straight (not helical) ribs would indicate Ishiwata tubing.