Well it is quite likely/possible that the brakes and front derailleur are first generation chorus from 1987. In fact given the year of the bike it is likely. What is more likely is that he upgraded the rear derailleur and shifters in 1992/93ish to the new indexing system which was far superior to the indexing systems of the late 80s. Is there a date code on the back of the cranks? Even if there is it's hard to be sure... I would make sense that he upgraded the cranks with the rest of the stuff but who knows... a date code might help with the approximate year, it'll be 2 didgits in a box. But no one seems to have a definitive answer as to late 80s date codes.