Notwithstanding the multiple flaws mentioned above (and those not mentioned), Tony is correct when identifying this as a Garde grenadier helmet. In WW1, an eagle like this one would be for a line grenadier, while a Garde grenadier would have the Suum Cuique center added. However, the Suum Cuique plate was only adopted in 1889 by the two Garde grenadier regiments. Since this helmet should be a 1871 model, it should be for a Garde grenadier (all line grenadier regiments were created later).
When you look at the picture of the inside, on the front side, it seems that there are at least 4 different screw attachments behind the eagle... what can this be?..