Slant six spark plugs and numbers

I thought that ZFR plug was for the older drool tube head?
I know that with the LA series V8's they sold a plug with the smaller hex (5/8) but Still have the seal washer and right thread length. When my son had his '90, with the 360 I thought they'd sold him the wrong plugs, I wound up calling Champion and was told that the plugs that my son bought were identical to the old standbys with the only difference being the wrench size needed.

But in the case of the slant 6, when they went to the peanut plugs, they went to the tapered seat instead of the flat flange with the washer. Don't use the plug pictured above, in a '75 or newer head.
Plugs that will work for a slant 6 for into 2 groups/ the 1st being for 60-74 engines and the 2nd grouping for 75-87 engines (never mind what year the car body may be)