William H. Curtis served in Companies A, B & E of the 84th Regiment Pennsylvania Infantry as well as Company I, 57th Regiment Pennsylvania Infantry. He received a pension for his services in 1907 = Appl: 1,369,468 Cert: 1,157,041 (misindexed in Ancestry as living in New Ireland rather than as it reads New Zealand).
I don't know if you are in New Zealand or what, but his pension file probably has much of what you are looking for. At the very least it should have where and when he was born. The National Archives in Washington, DC should have the file. To get a copy costs $75. However, Fold3.com (or Footnote.com) is working on scanning the files and making them available online, but this would require a subscription to Fold3 and they seem to be taking a very long time getting them done (you can sign up for a free two weeks if you are only interested in the one file when they get it done).
But I would start with where he died. I suggest getting his death certificate and obituary. Hopefully they'll also have the info you seek. The cemetery where he is buried and church he was a member may have some helpful data in their records.