Spark plug recommendation for carb'd 5.9

Same deal here. As delivered '00, 5.9, rpm intake, 650 edel. AVS, Hooker headers @ 1-3/4, in a '79 B body.
Chrome box ignition, OE vacuum advance distributor of unknown origin. (Which has to be worked on. To much advance in it. But....)
727/3.55's, 26-1/2 tire.

I am using the stock plug. Runs fine. Just get the carb & distributor
really dialed in well. Runs well on 89 octane.