Al, I revisited the page from my ggrandfather's diary where his entry for April 19 was, "Battle of Lexington, April 19, 1775. My great grandfather took part in it."
The key is *great* grandfather. I had forgotten that. At this point two of four candidates have been eliminated: Gleason and Barker; but who were the other two? Even time may not reveal the answer to this one!