Seat restoration of metal seatbacks

[Nifski]

I am taking the covers off our ‘64 and wondered if anyone has some advice. The metal seat bottoms are slightly bowed from people sitting on them of course but wondered how to flatten thes back out, seat frames are in great shape, no rust. Is this horse hair padding original?are the rubber stoppers original?

 

[pardion]

Horse hair is original as are the rubber bumpers.