I run the NGK BKR6E in my 505 , same plug in my 440 . 505 is 11:1.
Never any issues . Under 10:1 NA I would run -5
These are projected plugs.
Only thing with NGK's is they hate being over fuelled .

Tex


New best ET 10.259@129.65 .
New best MPH 130.32
Finally fitted a solid cam,
stepped it up a bit more
3690lbs through the mufflers
New World block 3780lbs 10.278@130.80 . Wowser 10.253@130.24 footbraking from 1500rpm
Power by Tex's Automotive