Warning...Crappy cell phone pics.
Here is the mold that Ed made.

Here is the product I am using. Much trial and error led me to this product. There are other products out there, however this is the only one I could find with different densities available. I went with a mid range density. I didn't want it to be too hard, but also not too soft either. I am told the original foam was fairly dense.

I've lined my mold with cling wrap, and am ready to mix my A and B portions. You don't have a lot of time between mixing and expansion.

After pouring the mixed foam in the mold, it is time to cover the mold.

Time is of the essence, as the foam will start to expand rapidly. (you can still see product on the mold from other foam I have tried with no success)

Relief holes for expansion.

Be careful, as the leftover product will expand.

And, Ta Da! The finished product. Just remove the cling wrap, trim any excess, and you are ready to install the foam to the headrest.

All in all, pretty easy. The next time I would use a drill to mix the A & B parts. I think you will get better, more uniform expansion. I may also try the lower density material and compare. With all the densities available, you could use this product to reproduce anything from stiff sun visors to soft seat cushion foam.
BTW, all the thanks goes to Ed Mason for making the mold and headrest prototype.
Damn I love this community!