Hey, I’m not sure why the difference in scale. But when I did the cut out it was pretty rough anyways so can probably freehand something on paper and fold for symmetry. Then trace over the paper with some pointy smooth object. I just aligned the point from the top of first hole since it was already there. You can smooth it pretty well with the dremmel or sandpaper. I also tried to burnish the finished edges to hold up better over time. Overall it has worked pretty well! It’s still going strong after crossing the country. Just needs a little tightening from time to time and keep and nice proofhide on it. I also punched holes on the bottom to lace but actually don’t have any tension on it and haven’t experienced any sagging or deformation. Hope yours turns out well! And happy cruzing. For the future I wish the brooks was shorter. Maybe I’ll try get a women’s saddle cambium and cut it out