...what about the PAM438 (tuttonero=all black!). Thing is, by the time these models were produced, the moniker Black Knight was already....taken

You'll just have to come up with another one and hope that's ALSO, not been given to some exsisting model :P
P.S. If you go to a Panerai GTG and mention the Black Knight, EVERYBODY will think you're referring to the PAM317