On all the pcar heads and early W-2 stuff there is a shorter head bolt in the upper row on each side. It would be the bolt that doesn't have the oil feed to the rockers going up through it.
To get oil to the rockers they made one stand taller on each head. It saved money even though it took three lengths of head bolts instead of two. Bean counters are weird.
The upshot is you can move the roof higher on one pair of ports on each head and not break into the bolt boss.
I just break through and then machine two spacers and epoxy them in. Then I use all the same length bolt/stud in the upper row. And the ports are all the same.
