I run Denso plugs in my engine. I had my heads out on the bench at work and had a Tundra in my rack getting a tune up. So I screwed on of the Denso Iridium plugs from the Tundra into my Indy head and they looked good in the chamber. So I snagged a set out of parts just to break in my 493 and surprise!!! they are still in there after about 6 years. They don't foul and never miss a beat EVER!!!
I'll never use another brand plug in my engine.Been using Denso plugs in all my engines since I've been an import technician twocents

Gus beer

64 Plymouth Savoy
493 Indy EZ's by Nick at Compu-Flow
5-Speed Richmond faceplate Liberty box
Dana 60