If it's a GMC engine, the first 3 digits of the serial number should reveal the engine. Serial number is on a machined boss just aft of the distributor. Should start with 228, 248, 270 or 302.
On AC plugs, the higher the number, the hotter the plug. Plug foulers are made to be used only on the plugs that are fouling, the can reduce fouling, but cost you some power from incomplete combustion.
