Ian, I am probably going to use NGK FR5 plugs that I have in my 440 6 pack. I think the NGK 'go' colder as the number increases which is opposite of everyone else, but those 6's you choose should be great for hard running. I had 7's in my Challenger and they fouled in less than 100 miles. Too Cold for my eds heads and my 6 pack tune,(68 primaries, 84 secondaries @ 12.9-13.1 AFR).... Run them for a while, pull them and try to see what they are 'doing' but it's going to be difficult to read them with alcohol and I'll have to rely on my Bosch Wide Band exhaust sensor on my 500 stroker project, to see if it's the right air/fuel ratio which will be around 9:1-10:1 AFR. Ethanol Alcohol with 15% gasoline is difficult to read on the plug insulator due to the lack of deposits. It burns very clean! I havent recieved my cylinder heads yet. I am going to buy them along with my computer this fall. 899.00 for the heads, 400.00 for the PCM,(Computer), I have to start assembling a Harness as well.
When I get my heads I'll start the porting and post those progress pics and my results.