You probably need to put in one new plug, in #7 cylinder, in the staging lanes close to pulling out for a time trial and shut the motor off after the run and pull that new plug out before driving it back to the pits and post a picture of it on here up scope twocents
What brand and spark plug part number are you using now?
How in the heck did you get a BB Mopar motor to make 520 C.I. with a 3 3/4 stroke confused shruggy

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)