You prob cannot use 7 speed indexed as indexed on 8 speed and Shimano also had a different 'pull' on some shifters/mechs in index so that the distance the cable was moved by the shifters did not match the required distance at the rear.(see Sheldon Brown)
With friction any shifter (within reason) will operate prrfectly. You can fine tune to perfect alignment and smoothly shift through the sprockets in one go.
I have always used friction and have run 7 , 8 and 9 speed levers with anything from 11 speed block to 8 speed with only 4 sprockets fitted.
Also you can interchange Campag , Shimano , etc etc as you like.
You prob cannot use 7 speed indexed as indexed on 8 speed and Shimano also had a different 'pull' on some shifters/mechs in index so that the distance the cable was moved by the shifters did not match the required distance at the rear.(see Sheldon Brown)
With friction any shifter (within reason) will operate prrfectly. You can fine tune to perfect alignment and smoothly shift through the sprockets in one go.
I have always used friction and have run 7 , 8 and 9 speed levers with anything from 11 speed block to 8 speed with only 4 sprockets fitted.
Also you can interchange Campag , Shimano , etc etc as you like.