^I believe that most healthy young men can get body fat in the 7-10% range from diet and lifting alone. But if you want to get below that, then you need to know some tricks. Could be wrong, though.
But basically, IMO, if Brad had any actual mass, he would have been in more or less "contest shape" for that movie.
I think Stallone could have walked right off the set of Rocky 4 and won just about any amature show.