FYI: The AutoZone near my house sells Motorcraft plugs. Maybe yours does also if Napa does not have them. Worst case the Ford parts counter will have them for a buck or two extra per plug
I can't help you with SPW none of my recent Mustangs had them.
Screw you and your coil over design
I dont have an autozone around me, i know it's wierd. I had to go to Ford parts counter where it ended up being like $4.18 a SP, when amazon has them for $2.53