Originally Posted by carsavvycook
It looks like you have problems other than just spark plug heat range.
You went bigger on the camshaft, and just a touch on compression. You will need to re-jet the carb richer, by a couple jet sizes, at least. The "very white plugs" says you are running too lean now. The "pop now and then at idle", says you might have a real lean mixture at idle.(possible vacuum leak) Also MSD recommends a plug gap starting at .050 to no more than .060, for their products to operate best. The fuel you are using will play a part in your tune.
A spark plugs "heat range" is determined by the engines cylinder temperature. In other words, a "hotter plug" is designed to perform best in higher temperature's, as in a "lean mixture". and "colder plug" would perform better with a richer mixture. The plug does not "burn" hotter, it will just dissipate the heat slower, keeping the plug "hotter".
You also changed gears, and converter which is going to have to be close, rpm wise, to the "grind" of the camshaft.
Perhaps I learned the wrong lesson sometime ago, but it has been my held belief that the opposite is true.
A hotter plug than required is detrimental in that it retains heat which can lead to expensive problems in a motor. A plug that is in the too cold heat range fouls easier as the heat from the plug is transferred too quickly to the cylinder head.
With this reasoning, I would believe that it would be worse to have a "too hot" plug in a lean condition than it would be to have a "too cold" plug.