Skip the NGK's and save yourself a TON of money..
Motorcrafe OEM replacements, or Autolite APP764 (double plats) are the ONLY two plugs I would EVER let touch your car.
Anything else is bogus (+4, etc) and the NGK's are too expensive to provide any difference in perforance, with a waste ignition system, causing the electrode to wear twice as fast as the rest.
NOT worth it, except with an FI application, etc. etc.
Ray