Shimano's derailers from the pre-indexed-shifting era aren't compatible with indexed shifting, which requires a specific cable-pull ratio (amount of cable pulled per the horizontal distance traveled by the pulley wheel) such that the clicks in the shifts line up to the gears on the rear wheel.
If you're talking about the model pictured here (about 1984, at the end of friction-shifting era), then you're out of luck as far as using it with indexed shifting.
Shimano indexing compatibility: all Shimano rear derailers since the advent of indexed shifting have the same cable-pull ratio, except for 7- and 8-speed Dura-Ace. So theoretically, you could use a 6-speed-era 105 rear derailer with an 8-speed system, etc.
However, derailers originally designed for fewer speeds are generally less precise (because they didn't need to be), and so you generally want a rear derailer designed for the same number of speeds, or a greater number of speeds, than you are using.
So a 10-speed-era rear derailer will be fine on a 9-speed system, but an 8-speed-era rear derailer won't shift very crisply on a 9-speed system.