The rear derailleur on my 79 French Record is a relatively rare long cage Shimano 600ex. The shifters are Suntour power shifters and the front derailleur is Suntour as well. There is another French Record with the exact same configuration that I saw described online. This mixed setup is unusual, and I wonder why they didn't use a Suntour Cyclone or Raleigh branded Suntour Vx rear derailleur?