Hi John,
I don't know if you found any but while browsing e-bay for Rover P6 parts (my other interest) I found this adverts and there appears to be a Volvo 164 in the background with rear headrests! Not sure if also being broken or not.
Hope this helps
Regards,
Adrian
http://www.ebay.co.uk/itm/Rover-p6-W...oAAOSwcUBYRDsY