Yes, I have.
Mine had the same symptoms. Once in a while it was as if there was a time delay in the ignition switch, I'd turn it off and a few seconds later the engine would shut down. I associated it to a worn ignition switch. Even with the switch in the off position I had a slight voltage reading at the ignition terminal. Then I installed a relay for the HEI powered from a junction block on the firewall and controlled by the ignition switch. This gave the distributor battery voltage on start up and 14.5 volts running. The problem intensified due to the relay needing very little voltage to close and supply the distributor with full system voltage. I installed a diode in the alternator turn on wire that goes to the idiot light and it cured the problem. The engine now shuts down immediately I turn the switch. the problem may have been solved with a new switch but I had a diode in my tool box so I used that. When I get a new switch I'll by-pass the diode and see if the run on starts again.

The dash warning light and/or the resistance wire with gauge should have enough resistance to stop feed-back from the alternator to the ignition but some after market ignition boxes and HEIs will run with even a little feed-back voltage. The diode is installed in the wire that runs from the ignition switch through the dash light and to the alternator. Install the diode with the stripe end towards the alternator.

It could be your problem is the switch, the resistance wire, the voltage regulator [if you have a stock type alternator and voltage regulator] or the dash gen warning light. Check all those fore proper operation.