Does your distributor have vacuum advance
The reason I ask, is that if you are getting pinging under light load, it could be the vacuum advance needs adjustment, or it is connected to the wrong vacuum source.
If not I'd suggest you graph your advance, and like D. Hearne said check to insure your timing is not coming in too quickly.
That pinging will definitely cause overheating. In fact if not taken care of it will eventually cause piston failure.
