I agree Gino - the ANH was used for ESB and ROTJ with minimal changes. The ESB was not moulded to create the ROTJ it was from an ANH mould and worked on.
Brian
This new information that the ROTJ came from an ANH mold is interesting...and just came to light because of the new helmet you have shown. If that is the case of course then the mounting rings/bases would have to be added on every ROTJ mask. We have a more than one person here including Don Bies that have been to the archives and should be able to say whether the ROTJ original masks there have added on mounting based or have them molded-in. I think I might have the answer but I'd like someone whose been there chime in.