Check the county court house of Talladega County since that seems to be the county he lived in and returned to to live after his service. Veterans were encouraged file a copy of their discharge papers (DD214) with the office that records such papers. It looks like the Probate Office does for Talladega Co. http://talladegacountyal.org/probate/probate_003.htm
Check with local VA affairs office if he used any G.I. benefits later such as money for school, VA loans, etc.
Did he belong to any local Veterans groups? Their membership records may have information (if they keep them this long).
Looks like he was in G Company in the 182nd Infantry.
I used Google search "Battle of Bougainville Hill 260" without quotes and found this in the many results:http://www.182ndinfantry.org/history/exhibits/show/182nd/pac...
Ancestry (fee) has Enlistment record but so does the NARA ADD online database website (free) that includes his Army serial number. If you didn't have it when contacting NARA last time then it looks like you got the standard answer. With it, file a Form 180 and be prepared to provide his death certificate and proof of next of kin. http://aad.archives.gov/aad/series-list.jsp?cat=WR26