1966/67 barracuda bucket seat interchangeability

66 and 67 barracuda seats are not the same. Nothing about them is the same. The frames on the 67 are slightly taller. The 67 has provisions for head rests, 66 do not. The frames are very different.

67 is pretty much one year only in A bodies so I would get the right seat for the car.

66 and 7 seats are the same for A and C bodies but not A
You covered the only differences I found between 66 and 67 a-body buckets seats. The back frame is slightly taller, its top member is round stock. 67 is formed to square with holes for headrests. 3/4 inch difference at most. Some of the early metal seat backs had a carpeted toe kick area. I don't think that carried over to 67.
I have 66 bucket frames with 67 skins on them in my 67 today. I had/still have the 67 verts bucket frames to compare to.