340 Pinging using 94

Update:

After adjusting the idle mixture screws, and retarding the timing, I got it to the point where it no longer pings at ~2k rpm.

But it does ping as I let off the gas and the car is coming down in RPM, around the 1,100 - 1,500 range.

The pinging is much quieter, but now is in the lower rpm range, and only when I let off the gas.

The spark knock noise is down to about 1/10th of what it was, it's just a slight tick now. As before it was quite loud.

Also, I tried changing the spark plugs out, and it ran TERRIBLE, and when I put the old ones back in it was fine again, not sure why or how.