Scoot your pinging might be carbon build up on the pistons, those old Mopars had a tendency to crud up. Does it have an EGR valve still on it? That will make them ping too when they are bad.
Get something turn burn that carbon off, ATF or SeaFoam nice and slow through the carb will take care of it, just make sure you are in an open area cause it will smoke like crazy!
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Chris
As close to "Normal" as I can get...
