Need 240V in the shop, is it already in this OLD panel box?

The big question is what's the amp draw on the compressor. There should be a nameplate on the motor.

As far as that panelbox, looks can be deceiving, as long as the box is not corroded when you pull one of the breakers off the bus. You can use forced air to clean that box up,

Once you deem the panel is not corroded, you can remove two of those single pole breakers and replace with a two pole breaker as long as the motor nameplate amp rating at 240 volts is less than 30 amps.

Voltage adds and current divides.