The actual prototype? Not that I know. But I can tell you that is Bob Dullams sculpt so he most likely was the one commissioned to make it.
I have a mold of the Bob Dullam cowl.
It is possible Bob did a clay pour of a production copy (or even from the original mold) then altered it. Bob is a great sculptor regardless so it may have been done from scratch.
You can tell the difference in this sculpt vs the production one by the mouth details.