340 Pinging using 94

Here is wat we need to know to begin to solve this problem.

What is the cranking compression?
What is the initial and total timing? And, when is it all in by?
What gears are you running? And, with what transmission? And, with what height tires?
What carburetor and does the tune seem dialed in? Or, are you experiencing any other issues?
What is the typical average operating temp of the car? ex, 195 deg..
What RPM are you running at 55-60mph.

Without that info, you are pissing in the wind.

I would get the timing locked down first. Set the total to 34 degrees to begin and make sure it is coming in no earlier than earlier than your 60mph rpm.