Hi Tom:
The helmet looks good to me. The domed spike base retainers and vaulted non-enameled Garde star make this a textbook example of a private purchase Diensthelm. For more information on this subject:
http://www.pickelhaubes.com/forum/viewtopic.php?t=867
I believe the helmet represents 2. Garde Dragoner Regiment Kaiserin Alexandra von Rußland. However, the domed brads should be gilt/brass.
I hope this helps.
Chas.