I've been using Accel 784 plugs. They take a 5/8" socket and fit my LA-X heads (Magnum type plugs) in my IHRA Dart as well as conventional Mopar small block heads which I have for a new NHRA 360 project.

I use to use N9YC and N7YC when they were easily found. But many years ago I found that the Champions seemed to rust if not run on a regular basis. I live in very humid Florida, but they didn't seem to be bad like that longer ago.