Best plugs for Magnum heads?

[64physhy]

I've been searching for a while to find out, but my head is spinning from all the info. I have Autolite 65's in right now, but had to modify a plug wrench to fit, and have now read that they will be a problem getting them in and out with headers (the engine is not installed right now). I want some plugs a couple steps colder than stock. Engine is a 414stroker, ported heads, step dish pistons, 10.0:1 CR, cam lift is .602/.611 237/242 duration, Airgap and a Proform 750.

 

[dgc333]

I use magnum specific plugs in my magnum headed 360. These are a 5/8" hex plug but the thread and reach are the same as your 65's. The smaller hex allows a socket to fit between the header tube and head easily.

I have a 10.6:1 360 and have tried the stock heat range Autolite 5224, the shorter nose 3924 and the colder heat range short nose 3923 plugs. There does not seem to be any difference in the way the engine runs so I have settled on the 5224 plug.