I made a 3d-model that fits over the head-base (version 21) that I posted at Thingiverse (http://www.thingiverse.com/thing:650760
) and printed it with my 3d-printer - sized for a puppet-head. I could make it bigger for the fursuit-sized head.
You can get this model on Thingiverse: http://www.thingiverse.com/thing:746225
I glued in a piece of yellow colored transparent plastic.
It's currently sized for a 16,5cm wide puppet-head - with enough space for the fur. I have not modelled the back of the head and the lower jaw yet, because the shape depends on how I build the head.