If you are looking for a period correct seat, look at BF Torino. BF-Torino.com
They make some really nice period correct seats that don't cost $3K each. The Recaros are like hunting for lost gold and those that have them want a fortune. That said, I would be concerned about seat height with them or any seat if you put it on the Pantera slider mechanism.
As for the comment on Hall seats, I am unaware Hall ever sold seats. If they did, they are no longer on their website. They only sell seat covers.