[68gmsee]

When I've had an engine ping it's been either timing, bad gas or bad or contaminated fuel.

First thing I would check is timing mark to make sure it's at TDC with #1 piston at the top of travel in the compression stroke.

Then make sure the vacuum advance actually works and does not have a leak or binding. I use a hand vacuum pump but in the past I have checked with mouth suction (shouldn't take much to make it moves).

And for grins, try a higher octane fuel to see if helps. Remember that octane is for retarding the fuel ignition to prevent the pre-ignition. If it helps with the pinging than the problem may be timing not advancing properly.