I measured all the places I could and created the following "blueprints:"
The side panels were a little difficult to identify exactly where some points start and end as the front and bottom corners are significanlty rounded, about 1/2" from the start of the rount to the corner. All the measurements for rivet holes are to the center of the hole.
One thing I found out as I pulled it apart was that there is a bracket under the bottom panel that has two guides to hold the side panels in place. You can see them in the image below.
The back part of the side panel just slide to the outside edge. There is no guide on the back.
One other thing. I did some research on what kind of tartan fabric this is. The closest I could come was that this was a variation of Campbell Dress Tartan. Here are a couple images of the tartans I could find:
I think it is closest to the second sample. I couldn't tell how to purchase this fabric or how much it might cost. My plan now is to try and find an automotive upholsterer who might be willing to tackle a small job like this. They may have access to more unique fabrics like this.
Well that is it for now. Hope this helps anyone who is thinking of trying to make one of these.