Here's some more:

The famed Georges Carpentier started his career out in the Flyweight division and actually ended up as a Heavyweight though he did start boxing professionally at the tender age of 14!
Evander Holyfield turned down a role in the movie Rocky 5 purely because his character would be knocked out!
Harry Greb versus Mickey Walker fought each other in 1925 and was actually filmed, however the footage has never been found!
Jersey Joe Walcott retired 6 times before wining a world title!
American John Rankin is the tallest ever man to enter a boxing ring at the size of 7 feet 4 inches!
Sam Langford and Harry Wills fought each other 23 times
It took as long as the era of Michael Moorer for a Heavyweight Champion to be a southpaw!
Marciano had the shortest reach for a Heavyweight recorded at only 68 inches
Oscar De La Hoya is missing the middle toe on his left foot.
Rocky Marciano was mistakenly registered as a girl by hospital staff when he was born.
Joe Louis was born with a full set of teeth.