I remember back in the 1968-70 years how the 426 Street Hemi always had plug fouling issues after some street miles where the 440 could charge on without issues. Was this due to the center plug location of the Hemi combustion chamber?
On our 1970 Hemicuda I remember when the plugs had been in a while the first time or two when you hammered it you would hear that top end misfire and fresh plugs would clear it up. Don't think the Hemis of that time were too rich at cruise due to the lean jetting needed for emissions and the
Street Hemi camshaft really wasn't that big in duration/overlap for an engine that size. Ignitions on both engines about same as far as spark goes. One of first things we did was install a CD ignition box on our car which helped a lot. Do remember having a cigar box full of used plugs out of the Hemi back in those days.