Antoine Bethea has been a successful pro for quite a while now. The safety started eight seasons for the Indianapolis Colts and was a rock in the secondary, known for his steady play and football smarts.But now that he's the new kid on the block with the 49ers, Bethea is just trying to fit in with a defensive unit that has been among the NFL's best.As the 49ers prepare for their opening exhibition game Thursday night vs. the Ravens, Bethea just wants to play his part.When he was asked in a radio interview on 95.7 The Game recently about his transition to the Niners, Bethea said he's simply "trying to fit in.""This is a veteran team with a lot of good players," he said. "I just want to fit in and do my job."Yet the 49ers are hoping Bethea can play a bigger role than just fitting in. In acquiring him to replace the departed Donte Whitner, now with the Browns, San Francisco is getting a player with 123 NFL starts, 14 interceptions and more than 800 tackles. The 49ers hope he can be a steadying influence and help make the secondary a cohesive, effective group.The other players expected to start in the secondary this season – second-year safety Eric Reid and cornerbacks Tramaine...