What heat range plug should I use for my 340???

I've had good luck with NGK V-power too. Your on the line for a 6 or 7 heat range. Start with a 7 and see how it looks after a few runs. May be fine or you may need to step up to a 6. My 408 is 9.8 to 2 compression and likes a 7
Hey fishy… I have a ‘72 Duster (built 340) with 11:1 compression. Do you think the NGK 7 (V-power) would be a good choice?

Thank you!