Mostly stock 340 engine what Spark plugs

IDK about anybody here, but I run the Champs in the ol'MoPars without issue. I'll leave'em in there for 3 years without thought. On a stock engine or mostly stock engine, unless you up the anti on performance and compresion, the stock plug heat range will do great for a lot of modifcations.

Once you up the comp. ratio and add a cam and so on, theres a possible change in heat range worthy of looking into. Otherwise, a stock plug will do.