If you look at the front of the brass crest and closer at the shape of the helmet two things seem evident.
Firstly the overall shape with ut's bacward leaning rake is of Minerva design.
With the peak also bring fur covered, I think this is an officers helmet of about 1813 and used in 1814.
The addition to the crest of a royalist silvered cartouche does add evidence to this possibility.
From 1815, The Kings Garde du Corps, Les Mousquetiers de Monsieur also wore these helmets with a white plume.
So......this could be a Royalist Garde du Corps Helmet recycled by a Cuirassier officier that survived Waterloo.
As such......I say original with a great history.
This Cuirass looks fine to me but new shoulder scales would give the item a longer service life legitimately up to the 1870's or even beyond.
Why would you throw away a perfect cuirass and order a new one when repairing it within the Regiment is easy.
Love all this
Paul.