Not to beat this up too much, but maybe its helpful, here's the pic of the K2 cases:
The mark to the right of the clip groove indicates that's the width of the single row bearing. See the space to the right of the mark? That's where the double row goes.
Here on the K4 cases, you don't see any marks as the dbl row bearing takes up the full width of the surface. As though it was made for the dble row to begin with...hmmmm.
But again there may be further upgrades on later engines that you are looking for?