Thermoquad 1966 Metering Rods

^^^^. This. Spark plug conversion charts [ between brands ] are an approximation. For Chry V8s, a '5' in the NGK range is best, in the NGK catalog. If road racing [ continuous WOT ] or using a power adder, then a colder plug such as a 6 or 7 may be reqd.
I am in the process of building a brand X engine that will have aftermarket alum heads. The heads use 3/4" reach spark plugs & are poorly designed; about 3/16" of s/plug thread is exposed in the chamber. The owner has another, running engine, with the same heads & he reports the plugs are tight to remove; because carbon has got into the threads. This engine would normally use a NGK 5, but going to use a 6 due to the very exposed position of the plugs.