Shimano has series designations for parts. The 1987-1989 105 was the 1050 series. In 1990 they introduced the 1055 series, which was 105 SC. Sounds like you have the former. All the major components should be stamped (usually on the back) with the part numbers, which will consist of the series number and a two letter prefix indicating the part type (i,e, BR = brakes, BL = brake levers, FC = crankset, FD= front derailleur, RD = rear derailleur, CS = cassette, FH = freehub, etc.). For instance, if you're looking for 1987-1987 brake levers with hoods, you want BL-1050.