Quote: What type of cylinder head? stock cast iron or aluminum?
If stock iron eads I would use a Autolite 74 or 75, try the colder #74 first and see if it and your local gas get along If aluminum then I would try the Autolite # 65 or 85(I think the # 85 are the restior plugs in 3/4 long reach, it is the same plug used in the stock SB Mopar heads )
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
If stock iron eads I would use a Autolite 74 or 75, try the colder #74 first and see if it and your local gas get along 
If aluminum then I would try the Autolite # 65 or 85(I think the # 85 are the restior plugs in 3/4 long reach, it is the same plug used in the stock SB Mopar heads 