Lets get a bunch of different wildly different opinions (or I hope not) on a spark plug choice here :lol:

540 cubic inch stroker motor (502 with eagle rotating assembly and .030 over)
afr 325v2 heads
intake duration 238
lift .66394
exhaust duration 243.3
lift .64567

victor 454-r intake
950cfm carb
merc manifolds and gil risers

stock thunderbolt iv ignition for meow

Looking for a starting point. I think I read the stock mercruiser 502's were a br6fs but there's like a billion threads with different numbers in all of them.

What's your take?

I've always used mr43's. Rarely fail and heat range is great. It's almost like asking what you prefer to eat for lunch. My opinion is only based on my own experience from NA builds near stock to wild builds to supercharged.

Looks like a marine kinetics combo. What did he suggest for plugs?

I know you are talking heat range with mentioning that plug, but just want the OP to know not to use that plug. The Ac Delco MR43's are a tapered (no gasket) plug, and his AFR's use a gasket'd plug, as most aluminum heads do.

I would probably start with an Autolite AR3935 myself.

Good call. I overlooked the AFR's.

ngk 5671-8.i like the ngk plugs.

I don't like black plugs when tuning.

you are not being politically correct,lol.

Black Plugs Matter!

(had to do it!)