[sc_rufctr]

The bottom cushion should come off once you remove the screws in the corners. If you think about it... What else could be holding it in place? The rear or back rest is a different story. It may have been upholstered in place after the cushion was built into the frame.

I wish I could see it IRL to get a better look (I've reupholstered a lot of stuff over the years).

That's a great looking chair with lots of potential.