[KingLT1]

I have been running NGK LTR7IX in my LT1 @ 9-11psi since 2019 with no issues. It's much higher compression with a much weaker piston vs a LT4. I am going to try Brisk RR14's next but point is the type of plug isn't your issue, but you do want a colder plug than a 5. A 6-heat range is stock for LT4 engines. I would do Brisk RR14/12 or NGK 7's for your power level.