I have had a couple cheap mountain bikes with 5 speed index. One even had a selector to go between friction and index.

thanks for all the replies. i've got the Sunrace 5 speed freewheel already. i guess the real problem now is finding a shifter which is as purty as the SA one. the shimano shifters are ugly IMO.

Did you ever get anywhere with this? I am considering trying to index-ify an old bike, currently equipped with a 5-speed sunrace freewheel and down tube shifters. I want to know if the shimano or sunrace MTB 5-speed indexed thumb shifters will work well with this - and indeed what derailleur might be suitable.

Using a non-indexing Suntour or Shimano rear derailer will usually index ok with any pre-'97 Dura-Ace shifter together with it's intended cog spacing.

A non-Dura-Ace SIS shifter will index with those same old derailers if the cog spacing is narrower by one increment than the intended cog spacing of the shifter.

A 9s Ergolever will index a 5 or 6s freewheel using a non-Dura-Ace SIS derailer.