You just need to run the wire off the IGN terminal on the switch to the +12V wire/terminal on the distributor. The wiring diagram for the MSD distributor should be on their website if you don't have the sheet that came with it.

The IGN terminal on your ignition switch is hot in both run and start positions.

On a stock 57 there is a wire from the R terminal on the starter solenoid which runs to the coil or the coil side of the resistor. You can and should remove this wire.

You may be thinking of the 55-56 switch which has an IGN 1 and an IGN2 terminal. One of those is hot in start, the other is hot in run. For HEI and most other electronic ignitions, you jumper those together on the 55-56 switch.