I picked up a NGK spark plug IMR9C-9HES. I got home and my book calls for:

Standard 'R0409B-8' or For Extended high speed racing 'R0409B-9'.

Obviously the one I bought isn't close to what the book says so I called the place where I purchased and he said that IMR9C-9HES is what it says in his computer. Does anyone know if it's ok to use the one I bought? These plugs aren't cheap.