Originally Posted by T-Mar

Being a Japanese market model complicates matters somewhat, as features can vary due to market preference. Most indicators are placing it circa 1986, with replacement Shimano New 105 brake levers (a common upgrade for the aero cable routing). Given the apparent age, it should be Miyata manufacture. However, I've never seen a Miyata serial number with one alpha character and seven numerals. I would have expected two alpha characters and five numerals. Did you check areas other than the BB shell? Sometimes manufacturers have serial number locations that are market specific. I've seen Japanese market Miyata from the mid-1980s with serial numbers located on the upper head lug/head tube.