I've got a 440 with Stealth heads. Compression is about 8.2:1 as it's a late '72 engine form an RV, but does have a forged crank. I running a Lunati roller cam with these specs:

Advertised Intake Duration: 270
Advertised Exhaust Duration: 278
Intake Duration at .050 Inch Lift: 219
Exhaust Duration at .050 Inch Lift: 227
Intake Valve Lift: 0.515
Exhaust Valve Lift: 0.530
Lobe Separation: 110
Intake Center line: 116

Running an FBO electronic ignition with one of their custom curved distributors tailored to this cam. My question is this, what heat range plugs should I be running? I use NGK and prefer to stick to these. The car is a heavy Newport convertible I use as a cruiser and freeway runner. Any suggestions?