521 SR71 spark plug recommendation

Hello all been a while since I’ve been on the site and had to create a new login. In the process of building a 521 with a set of SR71 heads and 13:1 compression for a drag boat and could use a spark plug recommendation. Thanks for your help.

NGK R5671A-8

How do you sit down with balls that big?
My neighbor has a jet boat that does 96mph in 660ft, every time he asks if I’d like a ride I tell him nope.....I’m good

It’s a fun ride for sure, a whole different ball game than a car. We run 102-103mph in 800 ft and 105mph in 1000 ft.