different size spark plugs???

hey i have a 2002 manual mustang v6. i had to do a heli core job on the head because i threw a spark plug out of the head. im currently breaking that engine down and saw that there arent many threads there compared to the other plug holes. if i were to drill them all out and tap them for a larger spark plug what plug should i go with? and by the way this is my spare engine so im gonna beef it up a lil!



someone told me to go with 5.0 spark plug size...


Thanks

Jake