Okay, so I was a bit discouraged because it really looked like mine was turning out to be freakishly wide. But I decided to pick up the Dremel and see where I could go with my little test model. Once I got to refining it, it looked much better but still too wide. Comparing it with the screen shots, I took some off the sides and refined the cheeks, and I think it's much better.
Keep in mind that I left some room for the wire, like on the eye notch, which is wider than it will be in the end.
Also while looking through the images I noticed that the teeth and bottom of the cheeks don't sit flat against the surface of the wheel like I thought. Here's how I reshaped it to reflect that:
Also note the shape of the teeth and how the outer ones are longer than the inner ones. All of this is from looking at the pictures.
I know the skull isn't thick enough (should stick out farther from the steering wheel), but after I discovered the quirk with the teeth and cheeks I'm going to add another layer of styrene to just the part from the cheeks up and I think that will be enough.
I'll be posting a final image of the outline when I'm done with the shaping.
-Rog