that serial number will be best clue for those who understand the code...but it's a Tange Champion #2 frame with long-point lugs, simple details, nice gray metallic paint, full-sloping forkcrown. Something along the lines of a good Univega or Miyata would be my initial guess

Pic assist (had to take screen-grabs cause Imgur won't let me copy)





weird top nut on this HS, nothing I've seen before