Note that 0.7.48 offers some new help in this case. The Manage authors dialog now has a button that will copy all the 'author sort' values to author. When you press OK, all the books will be updated. The attached screen shot shows the dialog.
You can get more information on how calibre manages authors and how to switch to LN, FN format at
http://calibre-ebook.com/user_manual...es-and-sorting