451 with 13 to 1 C/R... best spark plug

[Garys1969RR]

I have a 451, 14 cc dome pistons, 915 heads, 509 cam, single 4 barrel carb. I am trying to find the correct spark plug to use. C/R is about 13.3 to 1. The Champion RJ 12 YC I think may be too hot. Used to run a 413 with similar specs, and used Champion J 10 Y, which worked well, but cant find them today. This is a mainly strip car, occaissional street use. Any help appreciated. Thanks

 

[IQ52]

J10Y crosses to the NGK part# R5670-6. I was using the colder NGK R5670-7 or R5670-8 in my iron headed 451.