I don't think you can use a 3/4 reach spark plug with the stock 13/16 plug socket size, I'm almost positive you need to us the smaller 5/8 socket size plugs scope Champion plug numbers RN9YC versus a RC9YC.
Autolite resistor plug # in 5/8 size I use are 3921 and up to 3924 in my race gas motors and the same 5/8 size in non resistor # in retracted gap are 3931 to 3935, 3931 is very cold.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)