Why is this 360 pinging
Nobody mentioned the heat range of the plugs.
Good mention.
I'm with the fellas here starting with the above first. A stock plug or 1 step cooler is what I would run. I have had that short block combo before and it does like 93 octane better.
Next would be looking at the damper. If it moved at all. Then re time it.
If it was built properly, at zero deck height for the slugs w/a 72 c. Head, it is going to want 93.
Lastly, but not least importantly, look at the plugs for a rich lean condition. Re-check/jet carb, check for vacuum leaks at the carb, intake to head areas.
I would stick with the vacuum advance set up and limit the vacuum advance while keeping as much intimtiming as possible.