Thanx Scott,
I found the book "An illustrated history of the Missouri Engineer and the 25th Infantry Regiments" at Google Books, free for download in various formats. To download, you need a gmail login and password apparently. Free registration and a spare email account if you need one.
It is great reading and includes the list of all members including those killed in Centralia. I checked and found my James W Thomas, says he was killed in Centralia too. The book describes the organization, dates, etc so nice reading.
Tom Thomas