First, you will need to correct the paths on some of the guars with NIFScope, as some nifs are pointing to some wrong texture paths.
For the mounted guar only, you need to make an esp, with the guar entered. You will also need a riding script, there are several out there. Make sure you have all three of the mesh files in the folder you want to point to in the meshes folder. And the textures should be loose in a textures folder.