I've actually seen the 6-wheeled version at the Forney Museum, but I don't recall any signs or information there discussing the conversion (if any). My own opinion - and that's all it is - is that this is in fact the same car. I also agree that there's certainly room for the tag axle beneath all that Hollywood bodywork.
I've also seen the references here and there to King George II of Greece, and to the coachbuilder Binder of Paris . . . but really, who could blame either of them for not more strongly claiming a connection with this car? Unique it certainly may be, but beautiful it is not. Thanks for posting it, it's still an interesting story.