I bought a 1985 bike last year with Shimano 600 SIS (index) shifters on the downtube. It had a 6-speed freewheel which I converted to a 7-speed Shimano Tourney. I like to have my hands on the handlebars, so I swapped out the brakes and tube shifters for the Tourney brake/shifter setup. It's a basic setup, but it works very well. You'll definitely want to start with a drop bar bike - otherwise, costs can start to mount up.