Having just got my 75 the observations make sense. Mine has the short dropouts with the externally mounted springs for the axel stops. I am still able to have a smooth shifting high and low range with a 53/41 chainring set up and a 28 tooth low on the FW with a NR derailleur. For such a short wheelbase bike it tracks very well and has great stability in tight corners. I don’t know how much if any they changed through the years, but the person I bought mine from also had a 73 and said the ride was identical . That’s why he sold me mine.