There are a lot of self proclaimed experts out there....they are probably the ones who call the 400 Ford engine a "400M". No such thing as a 400M.
As for the FE, I've seen factory nomenclature in print that states it stood for "Ford Engine", to differentiate it from the "MEL" or Mercury, Edsel, Lincoln engine. But since it was first installed in the Edsel, it could just as easily stand for Ford Edsel as well.