There are 2 parts to the episodes containing the back / side shots of "George Steinbrenner" The first being either Larry David or Lee Bear were the "backs" of Steinbrenner you see throughout the series. It's not clear how it was decided which one would do what episode, possibly which ever guy was available that week for shooting. Part 2 is the fact that the "voice of Steinbrenner" was done by Larry David, who did numerous voice clips throughout the series, with the ocassional on-camera apperance. It's also known that Kenny Kramer who was the real life Kramer, could do an almost perfect Larry David impression so there may be an episode or 2 in which Kenny was the voice. However it can't be confirmed which episode contained which back / voice as there is no episode in which credit is given for the Steinbrenner character.