340 Pinging using 94

What octane? 91? 93?

First things first... check the cranking compression. If it's less than 180psi... its definitely a tune issue and not an octane issue. Imo but theres still other factors to consider.

Disconnect the vac advance, check timing. Idle and 2000-3000 rpm, check timing.

Let us know what both the cranking compression is and the timing, initial and full advance, with vac advance unplugged from the distributor.
then check the timing full advance with the vac advance hooked up.

Report back.