So the receiving hardware for each head rest costs $232.

I found a complete 60/40 seat back with head rests on ebay. I had to swap the brackets into the car's current seats since the ebay seats didn't match the car.

I made a thread about the installation here:
w123 Wagon - Adding Rear Headrests - DIY

Here's the finished job:

__________________
Chad
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys