By all means do NOT use toluene - it dissolves rubber, among other things.
Timing gears usually make a noise more like a rod knock, not a ping.
Load is immaterial but speed changes it.

You might try a very little less ignition advance.
Fuel pressure should be 28 psi, and if it is lower it would make it leaner
and more likely to ping.
You might want to check the valve lift. Should be over 3/8" on all valves.
If you check timing with a timing light, is it pretty steady or does it
bounce around or drift (at constant speed)? How is your ignition dwell?
The old distributors get harder and harder to adjust until you just can't
get the required dwell and still have the points break reliably.
Is your exhaust system open and air filter clean?
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma