I added rear headrests to my '85 wagon using the seatback from an '89 model. Just out of curiosity, I opened up the hog rings on both seatbacks to compare the differences - the '89 has special metal supports for the head rests, the '85 does not. However, the '89 seatback drops right into the mounts on the older wagons. Just make sure you get the latches for the top of the seat back from the donor car - they're a different design. It looked like you could put your old seat skins on the new backrest.

The rear seat headrests came standard on all 245s in 1989. They are removable so that you can fold the seat down. You just simply lift them up and out of the hole slots. To put them back on you again just simply slide the metal legs back into the holes. I've read somewhere that you can put rear headrests on the pre-89 wagons. People have done it. However, I believe there might be a safety issue in doing this conversion. If I'm not mistaken, the pre-89 245 rear seats do not really have a support brace within the interior of the backrest. In an accident, such as a rear-end collision, the legs of the headrests could dislodge from their location and angle out toward the passenger's back and thus possibly impaling him or her. I think you could transplant an 89+ 245 backseat to your 86 wagon. I believe the seats are the same shape and size for all the years.