Doug, at what throttle opening are you having the problem? I assumed that we were talking full throttle pinging between 2300-3500 rpm. Any other info about when the pinging occurs? Was the Pertronix installed before or after the distributor was reinstalled?

Unplugging the vacuum advance will affect the part throttle timing, not the full throttle timing, as it adds timing in response to vacuum. Light throttle, lots of vacuum and vacuum advance, full throttle, very low vacuum, no vacuum advance.