Retrofitting headrests to pre-1968 front seats comes up here every now and then.

I was throwing away the seats from my 140, so I figured I'd take them apart to see what would be involved to upgrade an early seat with the headrests. Just for future reference.

Although I never had reason to upgrade, I was curious what the proceedure was.
I've heard that the early seats were set up to accept headrests if desired.

So here is what the seat frame looks like. I can see that it would be a relatively painless proceedure aside from having to make that cut in the vinyl.
It is not required to remove the cover from the seat, however, in that case the bottom of the post mount would be above the vinyl. Maybe you could squeeze it under, but it might tear. Even removing the seat cover would not be super difficult, but it is not something I'd want to do regularly.

Note that these are 140 seats which have only about 8" center to center on the posts. My '68 122 has about 12" and the headrest itself is wider too.