Many people are obsessed with spark plugs. The choice of which plug to run is not nearly as complicated as the purists claim, unless you're trying to build a 100 point concours correct show vehicle. AC 43, 44, or 45 plugs were used as original equipment, with the "heat range" going up with the number of the plug. 43- - - -a "cold" plug mostly used for long haul highway driving which could dissipate heat quickly to the cylinder head and coolant to prevent the tip of the plug and the ground electrode from overheating and burning away. 44- - - -a "midrange" plug suitable for both short trip and highway driving, that has a somewhat longer path for the heat to travel from the plug tip to the shell that threads into the head. 45- - - -a "hot" plug suitable for short trips and/or engines that start and stop frequently without the engine getting up to normal operating temp every time the engine is started- - - -delivery trucks and cars driven mostly within city limits for short hauls. The 45 has a long heat travel path from the tip to the shell, resulting in the tip running hot enough to burn away deposits that could foul the plug and short out the spark path. "It ain't rocket surgery!"
Run an AC 44, or the equivalent heat range and thread length of any other brand of plug- - - -Champion, Autolite, Bosch, NGK, etc. The only plug brand I've had consistently bad luck with over 50+ years was "Prestolite"- - - -they don't last very long, particularly in a high performance engine. If you really like throwing money away for no good reason, buy some sort of "high output" plug like Accell.
Jerry
