I was watching MotorWeek, and Pat Goss had some suggestions for removing spark plugs. This was generic, not targeted to Mustangs.

He said to remove the COPs (or spark plug wires) and loosen each spark plug 1/8 turn. Then reconnect the COPs (or spark plug wires) and rev the engine hard one time. He said this blew out carbon that might cause the plugs to stick upon removal.

He also said that if you encountered resistance when removing the spark plug, do not force it. Screw it back in a bit, then screw it back out a bit. Keep doing this until the plug moves freely or you get it removed.

 

Good tip.

 

It would still be a good idea to use some type of penetrant (Kroil, PB Blaster, Deep Creep) as in the TSB,