I’ve seen the C7AE-A head on ‘67 model year pickup FE’s, I’m pretty sure that’s the primary FE head for both cars & pickups all through the model year, just my observation.
However maybe there’s a “loophole” for you - looking in the logbook of casting dates I’m keeping, the latest casting dates I have for a C6AE-R head is “6H3” & “6H4” August 3rd & 4th ‘66. They were from a Facebook marketplace ad, unknown what vehicle they came from, and that could have still been a ‘66 model year vehicle. But the earliest casting date I have logged for a C7AE-A head is “6G25” July 25th ‘66, so the casting period for both heads heads overlaps. And no idea either what vehicle that head was from, but I would assume an early ‘67 model year vehicle. I have quite a few “6Hx” C7AE-A head castings dates logged, so the C7AE-A head was certainly in full swing by August ‘66. I also have C6AE-U head casting dates well into July ‘66. Keep in mind my notes are just a small sample of the thousands of heads cast, and likely not the earliest or latest by any means.