All the info I have on John Marion Tucker came from the Confederate Soldiers Records at the TN state Archives. Godwin's company was assigned a letter designation after the regiment was formed. I think it was Company I. On one of the cards it states Company K, Whitesides Battery, but that was after he had been captured and exchanged a couple of times.
A great book is "Company Aytch" I can't remember the Author's name but he was in the 48th. It is well known and still in print. Also try this www.tngenweb.org/civilwar/csainf/csa48v.html.