Some useful links to assist in your search I suggest you contact U.S. Army Heritage and Education Center first and ask them to fax, mail or email a list of units that comprised the 28th, and then move on from there.
Do any of his war veteran buddies still live nearby, contact them for unit information.
The 28th Division association may be the next place to contact.
http://28thinfantrydivisionassoc.org/index.htmlhttp://28thinfantrydivisionassoc.org/index.html 28th Infantry Division Association may be able to help you 28th Infantry Division Association 1400 Calder Street Harrisburg, PA 17103-1297 Email: email@example.com 717-787-9385
A great resource for military history is http://www.carlisle.army.mil/ahec/index.cfmhttp://www.carlisle.army.mil/ahec/index.cfm U.S. Army Heritage and Education Center in Carlisle Pennsylvania U.S. Army Heritage and Education Center 950 Soldiers Drive Carlisle, PA 17013-5021
To make an historical inquiry or for research assistance Email: firstname.lastname@example.org Phone: (717) 245-3949