Thanks, Foxworthy. Mouthplate was pretty simple - just reasonably heavy-duty acrylic felt with a strip of gasket rubber on the lower jaw part to reinforce it and stop it stretching out of shape. I then put the red ultrasuede lining on top of that, and then a foam covering over the whole thing to give the fleece some support in the area of the head that was removed to allow the mouth room to hinge down.
Thanks, Muppetlab!
His lab coat arrived yesterday, but I'm still waiting for the fur I purchased for his hair to show up (tracking details show it's been in the country a week - Australia Post can be stupidly slow!)