I've seen images of them in Cinefantastique and American Cinematographer - dating from the making of the original film. So, they did exist at one time. They existed for all of the main characters, and were used, I believe, as stand ins during the lighting and preparation for the various wire-rig flying scenes in the first 2 films.
Of course, who knows what became of those filming artifacts, but they were in existance 30 years ago.
Hope this isn't redundant to info you already have.
Propstore of London sold a couple a few years ago. They got them from the collection of Stuart Freeborn. Propstore's Superman costume display mannequin which is on show at The Movieum of London uses one of the enhanced lifemasks. They are INCREDIBLY hard to get hold of and also expensive!