"March 13 or Bust"- Bob Arum

[Nameless]

How concrete is this site and source?

It looks quite true:

Fight news announced the same a few moments ago: Pacman agrees to fight Mayweather | Fightnews - Boxing News Updated 24/7

Rds.ca states the same: Mayweather-Pacquiao : ce serait fait - RDS.ca

Yahoo sports:Adviser: Pacquiao to fight Mayweather in March - Boxing - Yahoo! Sports

sports illustrated: Manny Pacquiao to fight Floyd Mayweather on March 13 - SI.com - Boxing