Ikki: "The ignition is standard with points and set to 6 degrees at idle and approx. 36 degrees under load"
.You could try to change the dist. advance curve using different springs.
. 36 may be too much. Drop it back to 34, then 32, and see if the pinging stops. Don't be concerned with the 6 degrees at idle at this time. You just want to see if the pinging stops. If it does, then you may need to limit the total advance to that number.
You can add a bushing or small piece of vacuum tubing to the advance pin : "M point type distrbutors made from 1955-1968 have a advance slot that is oval shape. The GM point type distributors made after 1969 have a advance hole that is nearly round. The shape of the hole for the advance pin was to changed in order reduce the amount of mechanical advance as the octane of pump gasoline was reduced. GM then started using open chamber heads with less quench area. Put a small piece of vacuum hose on the advance pin that is located in the weight plate advance slot and reduce the mechanical advance."
SUMMIT has a kit that will do both: https://www.summitracing.com/parts/mrg-928g/overview/
Ikki; "I have taken the vacuum advance away as this would go above 50 degrees."
PJ: Yep, it is supposed to do that for better gas mileage in cruising mode. It is important to have this. You can get an adjustable vacuum advance can from Summit and dial it in. Many say to use direct manifold vacuum versus ported vacuum as it may work better - something you have to play with.
PJ: Have you tried one step colder spark plugs? Use regular type plugs, nothing fancy like titanium tips, split fire, etc. as these are not made for older type engines and can cause too much heat in the chamber - and pinging.
PJ: Run a colder thermostat. Assuming your radiator/cooling system is in good shape. Just because the car has 36,000 miles, time has a way of corroding internals through electrolysis and you could have poor flow in your cooling system so as not to cool efficiently. Might want to get one of the hand held infra-red heat scanners and check a few spots around your engine to ensure cooling is uniform/adequate.
PJ: My experience with the older cars is that they can build up a layer of carbon, especially high compression engines. You have to blow out the carbon by opening the engine wide open a couple time, like accelerating onto the highway. Babying the car can cause problems and it just may need a good cleaning out.
Just a few thoughts on the subject.