I've got an '89 Raleigh with Shimano components I added - Tiagra compact crank with Tiagra front derailleur and Deore rear derailleur and 9-speed cassette - but the shifters are friction. I'd like to keep them downtube but make them index so I can make cleaner shifts (particularly in the lower gears).

Any idea what I need to add to make these index instead of friction?

Cheers,