BTW, if I should eventually want to convert my 1980 bike to index shifting, is this possible? I recognize I would need a new real wheel/hub for the cassette... but would a 9 speed cassette and hub fit in my rear dropout opening? I currently have a 6 speed freewheel.
Be more economically efficient to just buy a new 9 [or 10] speed bike.
frame is too narrow.. staying with friction shifting, 6~7 speed are compatible,
8 is 1 more added on the end of a 7 speed, needing more space.. Axle width thus frame spread.