A personell file will give you the greatest amount of information and there is no substitute for it. But there may be ways to piece together some of that information. He may have had his discharge papers recorded by the county recorder in the county he returned to. He may have had dealings with the Veterans Administration. The Purple heart means he was wounded so, he may have sought VA Medical care.Or VA real estate loans, educational benefits, etc. They would have recorded a certain amount of his military history to ensure he was entitled to the VA benefits he was requesting. This stuff is available but you may have to proove your relationship.