I measured the pockets on the back side of my OE 20" wheels, and they are 25mm deep.
If someone has the wheels off their SHO or Explorer in the near future, I'd be curious to know the wheel stud length from the face of the rotor hat to the end of the stud (front and rear, in case they're different). Otherwise, I will measure them in a few weeks when I remove my winter wheels and report back with the info.
Thanks!