But here’s where it gets tricky for the 49ers. With starting quarterback Alex Smith due to be a free agent on March 13 and the Colts not forced to make a decision on Manning until March 8, the 49ers could lose Smith if they don’t move quickly on Manning, who may not be fully healthy at that point. That’s why the best fit for Manning could be a team that already has a starting quarterback under contract for 2012, giving the team some flexibility because there’s already a Plan A in place. Then, that team could do either what the Jets did to Chad Pennington in 2008 or what the Vikings did to Tarvaris Jackson in 2009 and 2010, if this year’s Plan A+ comes to town. The 49ers could pull it off by re-signing Smith to a manageable deal, which would leave enough cap room to bring in Manning later. As Rosenthal pointed out Tuesday, Smith’s performance in the NFC title game could mean that the 49ers won’t have to break the bank in order to keep him around.