If your seats are in good shape and you're willing to do a little searching for headrests from a '68 or '69, All of the 122 seats later than '65, have the locating hardware in the seatback to add on headrests. A while back, a clever swedish fellow who's driving his grandmother's 122 explained in detail how he did this. I picked up a pair of bagged out '68 seats that I've been driving around for 3 years, while looking (not that wholeheartedly) for 240 seats.
I just did a search for previous posts about 240 seats (and didn't come up with much), but I recall folks here stating that there was a cutoff year after which the seats were either narrower or wider, limiting the usable 240 seats. I don't remember if it was the later or earlier seats that fit best. Someone here will hopefully be able to enlighten us. I have a 2 door and need seats that tilt forward, can weld and can't wait to have more comfortable seats.

I just went looking (on my hard drive) and found a PDF file describing how he did the headrest retrofit, which I will email to you. If others want this let me know.