http://www.packersnews.com/story/spo...-ers/13224513/

The Packers think he can, and on Saturday, the first day of training camp, Peppers and Matthews lined up together for the first time. Matthews, who didn't practice all offseason while recovering from a broken thumb, played mostly at left outside linebacker and Peppers on the right side, though both lined up at varying spots across the front seven throughout the morning workout.
So base it sounds like Matthews on left, Peppers on right. That would have been Peppers most common spot as DE, so it makes some sense for him to start there.