That is what I'm also confused.
Called My dealer in Poland and gave them my VIN and they also suggest Denso SK20R-P11 as a first fit in factory.
On US website appears SK16R-P11 and nobody could tel me why even in specialised shops ( they also suggest SK20R-P11)
I will get them soon and also Spatk Plugs ignition wires because I go On LPG so this is important staff.
If someone has a Good place to by things I need in UK ( London Preffered ) please let me know.
Best regards and Hallo on Forum as it is my first hope not a last post.