Sirrus was 105 equipped and that's 1987-1989 Shimano New 105 rear derailleur and calipers. but the crankset appears to be lower level and brake levers appear to be Dia-Comp/SunTour. So, it's been frankenbiked to an extent. The Sirrus did convert to a Unicrown fork for 1989, it was available in white in 1989 and the head tube decal is consistent with 1989, so a 1989 Sirrus is a definite possibility. The serial number should confirm the year.