Kyle Shanahan first called representation for former New Yorks Giants center Weston Richburg this past Monday.



The 49ers coach wanted a dominant new center, a player who could reprise the role of Alex Mack, whom Shanahan had enjoyed having at that position while coordinating the league-leading Atlanta Falcons offense in 2016.



So Richburg, looking for advice, phoned Mack himself.



Richburg told Mack that he was mulling his options, and that he was considering “joining Shanahan in San Fran–,” but he couldn't even finish the sentence — or the city name, for that matter.



“Do it,” Mack interrupted.



“That was enough,” Richburg said.



Richburg, 26, agreed to a five-year contract worth up to $47.5 million with $16.5 million of that fully guaranteed, and Shanahan had his upgrade at the center position. The 49ers traded former starting center Daniel Kilgore to the Miami Dolphins on Thursday...