I'm running 87 oct on my 1980 but I have the Omega ignition with advance curve 4 set. No pinging under any condition.
When my heads were rebuilt by boxerworks they replaced the valves with Black Diamond and not the seats. My bike is March of 1980.
I used to run Marvel Myetery oil in the fuel but now I am running Sea Foam to try and keep the alcohol from chewing up the rubber parts in the carbs. Fingers crossed...
I think the last time I replaced the diaphrams was back in 2000.