I have a Shogun I purchased new in I believe 1981, that I have upraded over the years. It has a sticker at the top of the seat tube Chrome Mollebendum with Double Butted across at a 45 degree angle. I think it is a 600 because the shifters, derailleurs, and brake levers are Shimano 600 arabesque parts. The serial number is M9J20794. Any info would be appreciated.