Interesting! It has the 1989 only Deore II rear derailleur but 1988 Deore shifters. The crankset could be either year, as could the brake levers. I can't see the other componets well enough to determine if thet are Deore or Deore II. So, was the rear derailleur upgraded or the shifters (and cassette/freewheel) downgraded, or did they simply cut some costs by specing Deore II with 6 speed, as opposed to the normal 7 speed? One thing is for sure, it not's 1984-1986, as U-brakes weren't available then. The serial number and/or pics of the front derailleur and brakes may help to decide the actual year.