Someone already said Keith Miller. VFL star and state representative with St Kilda before abandoning football to become Australia's greatest cricketing all-rounder and one of the inaugural "legends" of Australian cricket. Miller was truly elite at two vastly differing sports more so than Anthony anyway.
http://en.wikipedia.org/wiki/Dean_Brogan This guy is not in Mundine's league at all. But, Won premierships in both codes DURING Choc's career in both sports. Funniest part is, he doesn't yearn respect. Crows fan at the airport had a word to him and the story goes, "If you say that one more time I'll whack you." So he did. And he did.
There's a reason fighters of old could fight 3 x 15 rounders in a month, it's called a lack of intensity and athleticism. They were essentially marathon runners in a boxing ring, no explosiveness, just two guys who train like grandmas playing rock em sock em robots in the ring. Old school boxers and training have gone the way of the dinosaur for good reason. They could give up massive weight advantages because the bigger guys trained like idiots as well, running in boots and avoiding weights in case they accidentally became an athlete with power.