(This is Part 1 in a series that will spotlight five 49ers players to watch Friday night in the team's exhibition opener against the Minnesota Vikings on Friday night, 6 p.m., at Candlestick Park.)All the starters are back on defense. And most of the starters return on offense. The most notable exception is at right guard, where the 49ers will have a new face.Alex Boone has never played right guard in his life. This will be his first opportunity to showcase his play against an unfamiliar opponent. It's going to be Boone's position to lose, as the team prepares for the regular-season opener Sept. 9 at the Green Bay Packers.The 49ers can only hope Boone sees a lot of Vikings defensive tackle Kevin Williams. Boone could benefit greatly from going against Williams, a 10-year professional and six-time Pro Bowl player. But it's doubtful Williams will see much action. And Boone might not be on the field for more than a series or two, either.The 49ers have placed a lot of trust in Boone's ability to adapt to guard. The organization made no attempt to re-sign Adam Snyder, who finished the season with a string of 15 consecutive starts, including both playoff games. They also did not offer a contract to Chilo Rachal, who began last season as the starter, struggled and was replaced by Snyder.Instead, the 49ers determined that Boone would be a better option. Boone was the 49ers' swing tackle last season. He is learning how to play in tight spaces. He said the key to playing guard is to become a mauler.So far, he has performed well in camp. But if he falters, veteran Leonard Davis has performed well enough to receive serious consideration for the job.