These port photos show the difference in the vertical port location between the early and late heads.   The intake port floor was raised and the exhuast port floor was lowered. Raising the intake port floor increased low speed air flow for reduced emissions. The exhaust port floor was lowered to help fit the FE into the Fairlane and Mustang chassis.

The floor of C4 intake port is 0.484 inches from the deck of the head while the C8 port floor is 0.871 inches from the deck.   The two ports shown in this photo and the difference is shown by the calipers in this photo .

The exhaust port is lower on the C8 head.   The exhaust port floor is 1.154 inches from the deck.   The C4 exhaust port floor is 1.406 inches from the deck. Unlike the intake port the size of the two exhaust ports is the same; only the locations changed.   The two ports shown in this photo and the difference is shown by the calipers in this photo.

Note that the CJ head is the only late - after 1966 - head with the tall intake port.   All of the early heads - pre 1966 - had the tall port however.   1966 was a transition year and the FE used several head castings including C6AE-J, C6AE-L (rare), C6AE-R, C6AE-U.   The C6AE-U is the same as the C7AE-A and very similar to the C8AE-H and the D2TE-AA.   CJ head casting numbers are C8AE 6090-J (before around January 15, 1968) and C80E 6090-N (after January 15, 1968.   The C6TE-A and C6AE-R are the only two tall intake port heads for '66 and '67.