Dieseling is caused by something hot in the combustion chambers igniting the gas. This causes the engine to turn over creating vacuum which draws more fuel out of the carb (just like it was running) which enters the combustion chamber ignites and continues.

If the voltage to the MSD is switched off it has no effect.

The most common fix from the factory is to use a solenoid to set the idle speed. When the ignition is turned off the solenoid de-energizes and the throttle plates completely close and it will stop dieseling.

High combustion chamber heat can be caused by lean mixture, ignition timing, or high compression.

An alternate is to shut the car off and then hold the throttle open. The dieseling will not allow fast rpm's (in most cases) so the vacuum drops and the fuel stops being drawn out of the carb.

I prefer the solenoid option if available.

or EFI