I am out of my stockpile of OLD STYLE AC Rapidfire #1 plugs. Looking for a new plug to use. What are you guys using? BBC 489, 500HP with cast iron heads 8.9 to 1 compression Fuel injected.

I'd run AC R43TS

Funny story, you turned me on to the Rapidfire plugs about 10 years ago. When they changed them I bought about 4 sets of the old style.

That was a LONG time ago, like 18 years
I ran the Rapid Fires in my 24 Outlaw because they idled better and didn't foul out at idle in heat and humidity.
The R43TS is the same heat range and it has a slightly extended tip over the normal MR43T.