Interestingly enough, I scavanged a bunch of 105 components off of a scrapped Centurion frame the other day. It had 105 indexed downtube shifters, a 105 rear derailer, and a 6 speed Shimano freewheel with primitive shifting aids (mainly just a shortened tooth every 90 degrees on the cogs). I don't know for sure if this was the original equipment or not, unfortunately.