It turns out somewhere along the way Ford changed the head design on the Triton and changed the way the spark plugs seat in the head. This affects how the insert tools cut, or don’t cut, the seats for the insert.
You can read the Timesert paper on the issue here here
I posted a video of my heads here
According to Timesert the problem heads have the casting mark with a 1L2E in the casting number.
PROBLEM HEAD
The problem heads have a step which prevents the seat cutting tool from registering properly in some insert kits.
The casting mark on the heads of my truck look like this
I blew up the image and inverted the color so I could see the numbers better. No 1L2E on my heads. Looking down the spark plug hole with a bore scope on a fresh, uncut spark plug well shows a smooth sloped transition from the well wall to the spark plug hole.
It turns out the Timesert kit I purchased, the 5553, accommodates both head styles, but it’s nice to know what you’re working with before you start cutting.