Note that the 105SC drivetrain parts date from at least 1990 or newer and so are newer than rest of the frame. I wouldt worry about retaining them for originality as they likely were not the originals, probably added as an upgrade for index shifting.
http://velobase.com/ViewGroup.aspx?G...1-8c1cabc9f04b

Wheelset and brakes are also much newer.