I found some potentially useful information with Google Book Search:

"Ozark Folksongs," by Vance Randolph, contains a version called THAT LAST FIERCE FIGHT, with the first line, "'Twas just before the last fierce fight."

"Country Music Records : a discography, 1921-1942," by Tony Russell et al., 2004, lists a song called JUST BEFORE THE LAST FIERCE CHARGE," recorded by Green Bailey.

There is a text called THE TWO SOLDIERS contained in "Covered Wagon Days" by by Arthur Jerome Dickson, first published in 1929, based on a diary written in 1864. Click here to view.

There is a text called AT FREDERICKSBURG contained in "My Diary : The Lost Civil War Diaries : The Diaries of Corporal Timothy J. Regan" 2003. Click here to view.