340 Pinging using 94

Higher octane resists pre-ignition but will not stop it if conditions over run its ability. If you can hear it chances are its starting sooner. I would avoid additives and dig into the timing, distributor, tune and carburetor/fuel system until its sorted. Unless you got a really bad tank of gas? Did the car sit for some time i.e. old fuel?

When you say its loudest at 2k, is that at cruise in 3rd (assuming 727 or 904) or if you go WOT and it pings before it kicks down?

Do you have a vacuum gauge and timing light? Does the trans have a higher stall converter?