I would definitely agree with the 17th century European identification: the large steel neck gorget (with a ruff thereunder), the plumed type of hat, the decoration on the sleeves, the type of sword hilt/pommel, etc. Superficially, I can see your thoughts as to a vague resemblance to the American Civil War cavalry/officers (when some fantastic variations existed). However, the extensive gorget was not a "typical" American accouterment of that tme, and would have been viewed as quite old-fashioned/obsolete. IMO, I do consider this costume to be of/in the 17th century style. Regards, AP.