The indexing is in the shifter, not the derailleur, so there may not be a problem. The chainrings, cranks, and BB will be no problem, and the front derailleur should be fine too. You shouldn't have to replace the freewheel yet. I have an 89 Cannondale M400 with Suntour XC-M, and it still runs fine. I replace chains relatively often, since they will wear faster with an older drivetrain, but it still runs and shifts without any major hiccups. Just a note for the future- it may be more cost effective down the line to replace the whole bike, rather than part by part as things eventually reach the point of no return.

DEMON