I am grateful to Peter Farina for the following suggestions for making the mogwai from US letter size paper:
1. Make the box/paws as described (w/o step 2-3).
2. For head #1, cut a sheet of 8.5 X 11 paper in half lengthwise and then cut a square from it. This results in a 4.25 inch square. The head is slightly larger than the original size. It may be a bit oversized but still looks OK.
3. For head #2 you could use the same method to get a 4.25 inch square, but it will be slighly smaller than the original size and I think it is too small. It looks much better if you measure and cut a 5 inch square.