Someone on the ancestry.com message boards got me a PDF copy of Heitman's book - I found out that there was no Lt. Thomas J. Durvin - instead the person was actually "Durnin, Thomas James. Pa. Army. Pvt corpl sergt and 1 sergt G 2 drgs 14 June 1855 to 1 Aug 1861;
2 It 16 inf 14 May 1861; 1 It 24 Oct 1861; r q m 21 Nov 1862 to 3 Mar 1863; capt 8 Dec 1864;
trto 25 inf 21 Sept 1866; bvt capt 19 Sept 1863 for gal and mer ser at the battle of Chickamauga
Ga; cashd 21 Sept 1867".

The name was apparently 'mis-transcribed' on ancesty.com as 'Durvin' when it was really 'Durnin' - Sorry - false alarm! Glad to know that he was not one of the Virginia Durvin family.