I don't know where you got 3515267 from. But it points to a different mad scientist with messed up textures. If you encounter a black model, follow the video, when you're reading the .mo3 file, you'll see some .webp files, these are the textures that you will need to apply to the model on wow.tools. So for this mad scientist, the .mo3 is 124827. Search that, then in the textures tab in the top right, you'll plug in the three .webp file names you see in textures 11, 12 & 13. 11 = 124826 12 = 124828 13 = 124825