The Cowboys have also reportedly agreed to sign linebacker Justin Durant. However, before either move can be made official, the Dallas front office must do some maneuvering to free up enough cap space.
According to the Dallas Star-Telegram, a player will be cut Wednesday and another player's contract re-structured to make room for the two signings.
In nine seasons, Allen has 33 starts between the Steelers and Buccaneers. His best season came in 2006 with Tampa Bay, when he compiled 77 tackles and started all 16 games.