With the skull itself nearly done, I have turned to adding a base to it.
Here I have cut out 15 layers of .06" thick acrylic, which blend from the backside of the skull to more of a face shape.
It's hard to really see it in the photos, but this will be part of the skull when it's cast in resin. The acrylic was glued together, and then I smeared Bondo™ auto body filler all over it, let it cure, and sanded it down in order to make a smooth transition between the layers.
The bottom of the base flares at the sides to accommodate the cheeks, and the top is shaped for the nose. This will attach to a strip of leather which will actually touch the face.