I finally got up the gumption to speak on the phone with my father's uncle; his mother's younger brother. This man was a general practitioner for many years in the Hyde Park neighborhood of Chicago; he served in the US Army Medical Corps in WWII, and his unit was overrun by the Germans in the Battle of the Bulge. He came back from Europe with several "trophies", including a foraging cap from a German soldier, and a set of field glasses he got from a German lieutenant. He was my father's favorite relation of his generation, and he treated my Dad as a younger brother.
He didn't seem to recognize me on the phone.
Sad. But I'll try again in a week or two, and I intend to keep it going.