Stuck 1970 Dart headrests

I bought a set of seats from a friend's '70 Swinger 340, already reupholstered with Legendary covers. The headrests on the front bench are raised and will not go down. I've hit 'em pretty hard--as hard as I dare without damaging the headrests--to no avail. I'm guessing he goofed something up during the reupholstering. Has anyone run into this issue that can give me an idea of how to fix it? I'm not keen on removing nearly-new upholstery, but I'd like to be able to raise and lower the headrests.

Ideas?