Well guys I spent an hour this morning looking through two books in the collection, Les Coiffueres de L'Armee Francaise by Margerand and Plaques de Shakos by Blondieu and this helmet plate does not show up. There are several that are very close, multiple fluer-de-lys with a crown above, but no large single one with a crown. I even looked through Kube's book Militaria thinking something would show up there, dry hole. I do not speak or read French so there may be a detail in the written portion of the books that I am missing.
The two French books I named here are excellent references and go into incredible detail showing the amazing amount of variations/changes in headgear plates (plaques), and other important details, which appear on French examples from 1791 to about 1900. I would have thought for sure something would have been shown there #-o
Someone's gotta know....Royal Household helmet of some type...or????
Larry