spark plugs
 

I know this has been asked a thousand times but what type of plugs should I run? I will be pulling an engine to do alittle work and this will allow me to reach and change plugs in both engines.Running NGK br6fs plugs now . No reason just was told to.
Engine info: 454 mark 4
square port LS7 heads
9.1 compression
eldebrock performer 750 marine carb
Stock merc alum dual plane intake
gil exhaust
Billet roller cam. from RM builder. Don't remember grind.
Roller rockers
Motor dynoed 449 hp @ 5300 rpm.
NGK BR6FS plugs gapped at .035
Timing set at 8 degrees initial
thunderbolt module 24 degree

Motor never run over 4700 rpm. Most always cruise in the 3700 to 4000 rpm range.
Just wondering is there something better I should be using. I cannot just "change plugs" when I want
because with engines installed I cannot reach the plugs between engines.
Thanks