Really cool you found his QSL card on ebay! Unfortunately I don't have many ideas. Do you know if he was affiliated with a college club at some point? I did some ham-genealogy work several years ago for my old college club by searching the school's library and found a surprising amount of information. You might also search the county library system for his name or callsign. They've done a great job of digitizing and making searchable all the old microfiche etc.