Appreciate some input on spark plug reading

The heads are probably the limiting factor if your tune is optimized. I go down one jet size in May and another one down in July when it really gets hot and humid. The higher the humidity the lower amount of oxygen available to burn. My car runs best @12.4 flat fuel curve with the O2 sensor I currently have on 93 pump. Most folks just run pig rich all summer and dial slower.
You are at the mercy of whatever the quality the fuel is on the day you fill up. WaWa 93 is what I've been using lately. Find a station that sells a lot of fuel. Race gas is always the same quality so keep that in mind.
- Make sure your carb is sealed to the hood scoop to prevent hot under hood air from entering.
- A return style fuel system will keep the fuel and carb cooler.
- A dash camera mounted to view the important gauges helps to review after the run. (poor man's data log)
You may also want to calculate the converter slippage at the stripe in third gear. Wallace racing has all the formulas for that.