The serial number is consistent with Merida of Taiwan. While I agree that it looks 1970s, the serial number would suggest 1971 manufacturer which I believe is too early for Shimano SF dropouts. That suggests 1981, but the lack of braze-ons would be curious for this period. Generally owners don't repaint over chrome and the apparent lack of chrome on a bicycle with forged droputs is typically more indicative of 1981 than 1971.

There were some brands manufactured in Japan with Columbus tubing, notably the upper end Lotus models but the tubing is more likely an Ishiwata or Tange set. If you remove the fork there should a manufacturer's stamp and possibly a date code, stamped on the outside of the steerer tube. Also check for the presence of splines on the inside of the bottom of the steerer tube and report the quantity and style (straight or spiral). Finally, the diameter of the seat post is often a good clue as to the grade or rough level of the tubeset.

Almost forgot. Are there any headbadge rivet holes in the head tube, If so, how many and what pattern? What's the spacing betrween the rear dropouts, 120 or 126mm?