You've captured the look very nicely Steve. I've always thought the best replicas had a very narrow edge at the point where they touch the side of the chair. Yours have done that.
I think that from an upholstery point of view the challenge will be to staple the fabric properly on the inside of the front facing curve. I'm sure that there is a special stapler that can reach into that small space but I've never seen one and that is why I've not attempted this project.
With my experience assembling Madison replicas I've found that sometimes you have to put a panel on as you go. If you attached the fabric at the front while the back piece of plywood was off then maybe you could slide the plywood in last?
I will be curious to see how you are able to overcome this. Hopefully it won't be a problem at all.