Technical Spark Plugs for 601 heads?

I have a 70's 305 with early 80's 601 casting heads. All new internals, Lunati .458/.284 cam and lifters, 9-1 compression. I've narrowed it down (at least I think) to Autolite AR133-135. Just not sure on which heat range. At 5 bucks a piece I'd like to get it right. Anyone have any recommendations?

 

AC R45TS is only $1.38 each at rock auto, and will probably work pretty well.

what crosses over to that, in the Autolite brand?

 

Crosses over to an Autolite 26, but it's a heat range 6. Might be too hot.