Counter flow heads for me are heads that share the same inlet and exhaust path . There wasn't too many of these engines built most were experimental . One such engine was a reverse boxer , so the pistons faced inwards and ran off two outer crankshafts . Both the inlet and exhaust flow came from the same ports . I'll have to go through my engineering text books to find some more information on it cause its been a while since . This engine is similar in a way : https://en.wikipedia.org/wiki/Junkers_Jumo_204
I generally call heads cross flow or non-cross flow . Reverse flow is another name : https://en.wikipedia.org/wiki/Revers..._cylinder_head