340 Pinging using 94

I have a 340 in my 72' Duster

I have had some pinging issues recently using 94 octane pump gas, and am going one of two ways to try and resolve the problem. I just wanted to post it on here and see what y'all think.

1. Lead substitute fuel additive/octane booster
2. Use a lower octane fuel (91,89,87)

I have tried retarding the timing to help with the early detonation, this helped a little bit. The pinging is not as severe, but it is still there.

Let me know what y'all think, your knowledge is much appreciated!