My shell is also 29" by 20" and it looks like My Durant M2's Shell. Pretty much identical if you look at the above picture. So I am guessing this should fit all 1928 Durant M2's. I wouldn't mind having an extra but I Can't afford it at the moment.

I can see about the guy with the Durant in the box.
Gerald.

Where Are You From? BC

Do You own a car built by Durant? Durant M2

If you post a pic here I would be happy to tell you if it looks like my 28...
Also a few measurements. What did you want for it? I know another guy with a 28 in boxes.

Where Are You From? BC

Do You own a car built by Durant? Durant M2