Originally Posted by T-Mar

Welcome to the forums. Based on the serial number, your frame was manufactured in 1980 by Miki of Japan. While it could be a Shogun, Miki was a contract manufacturer who built bicycles for numerous companies, so there are many other possibilities. The 600EX drivetrain is era and source appropriate but I wouldn't expect the Weinmann brakeset and rims on a Japanese manufactured bicycle of this era. The 600EX drivetrain, assuming it is OEM, would indicate a mid-range model. Photos may help in identification.