He would struggle fitness wise.
LBJ's fitness levels are perfectly designed for him to sprint 20 odd meters down the court, jump, change direction etc. He is exceptional at using maximum energy over a 20/30 second burst.
However, with an AFL ground much longer and breaks in play less frequent, he would struggle (at his current fitness level) to sprint 50 meters, then handball or kick, then sprint again etc.
Remember that fitness programs are different in Basketball than they are in AFL (In Basketball, shorter sprints and required whereas AFL requires longer sprints and less rest.)
Thats just my opinion from a fitness perspective: He would have the size, speed, leaping ability etc to absolutely dominate.
But this wouldn't come out if he lacked the AFL-type fitness level.