The subject bicycle appears to be equipped with Shimano RX100. The only years it came with RX100 and this style of frame was 1991 and 1992. In 1990 it came with SunTour GPX. In 1993, it came with SunTour SL derailleurs and the frame was updated with an extended seat tube and was only available in blue. I don't have the 1991 catalogue but 1992 came in that colour scheme, which was called Meteorite Melt Red w/Yellow. The serial number should tell us the exact manufacture date. Neither the 1992 or 1993 literature shows the subject boss.