If you have a 302 that runs on pump gas then you have a compression ratio of about 9 to 11 to 1 and since you run it on the street you also have a cam that is suitable for a street car. I will assume that the AFR is around 11.5 to 12 to 1 and total advance is 32-34 degrees. Pick a spark plug that works best based on the fuel requirements. That's pretty much it. I see no need to change spark plug heat ranges unless you are retuning the engine parameterizes for track use. I also see no need to to do that on a street/track car. Once you have the AFR dialed in across the rev range, that's it. That engine is tuned to run as best as it can. Then the plugs heat range need to suit the engine. Spark plugs don't make more power. They certainly can make less if selected incorrectly as well as damage the engine.
I will add one exception. Boost ....... if you have a boosted engine and run more boost on track then of course different plugs are part of the retuning. The other thing that might also require different plug selection might be altitude. If you live in Reno and take your car to Sears Point then a retune is in the cards for you. Reno is about 4700 feet and Sears Point is a less than a hundred.
