Hmmm, not really sure. I just sized it to the 26er had on hand at the time. I gave it away when I sold that 26er a while back. I have another 26er with a real live SnS. It's not that hard to mock up, no real rules to how wide as long as the shoe fits. The SnS is 22.5" wide at the pointy ends, why not start there? Depth (I mean height) is the same as the Weber basket. Depth (now I mean depth) should be close to 7.5".
Marty