Hi Chris,
Had a wee look at the hear rests on mine. They're original and built in to the seat backs, adjustable up and down but don't seem to come out. :

: Haven't seen too many on 126's.
Now if only I could get this one to go and persuade the tax office to "import" it to NI I'd we'd be flying ..erm I mean driving....
ausitn/gnash