I got the eyes from Van Dyke Taxidermy. As Jonathan said, half a wooden egg makes a good start for a skull, supplemented by Sculpt-a-mold, a cellulose based product similar to paper mache to which you add water. Here's what it looks like - I used a Dremel to shap pockets for the eyes





One of the biggest tips if you have a tanned pelt is to soak the head in water long enough to soften the cartilege in the nose and ears so you can "pop" out the nose and ears back to their natural shapes, positioning the ears to look natural. This is what I failed to do on the skunk I made. The same with the claws. this is what you typically get with the pelt



after soaking the claws and doing any sewing or other repair, you let them dry like this