Dr Rieck says the following:
…once and for all.
First, the 77/78F2/3 heads shared a common head drain back hole which early K,F and late K heads did not.
This eliminated the middle drain back holes in the F2/3 heads.
The 4 studs next to the eliminated drain back holes require cap nuts and copper sealing washers on the F2/3 head only.
The late F2/3, 77/78 cylinders CAN accomodate the knock pins(or dowels) and the rubber gaskets which allows you to run these early/late K and earlyF/F1(75/76) heads.
The later F2/3 castings are good as they are more stout but this does add weight.
Trying to run a Wiseco 836 kit with an F2/3 head will result in low compression secondary to the increased volume of the F2/3 chamber.
Bottom line….early/late K and early F1(75/76) heads will work on late (F2/F3) cylinders and early/late K and F1 upper cases with mild opening (joining) of the F2/F3 two inner drain back holes at the base of the cylinder