According to The Hollywood Reporter, Dickens is in place and Zahn is in negotiations for "Treme," which takes its title from an area of New Orleans.
Zahn would play David Rogan, a street dancer, radio DJ, band member and Big Easy native. Dickens would play a chef and occasional love interest for Zahn's character.
Simon previously cast Clark Peters, Wendell Pierce and Khandi Alexander for the pilot.
The trade paper notes that Zahn has long been a target for TV casting directors. Best known from roles in films like "Rescue Dawn" and "Sahara," Zahn was seen last month in an episode of USA's "Monk." His other TV credits include the CBS telefilm "Comanche Moon" and a memorable guest spot on "Friends."
Dickens is a more familiar small screen face. Currently appearing on NBC's "Friday Night Lights," she co-starred on "Deadwood" and appeared in the premium cable network's unaired "12 Miles of Bad Road" and the pilot for "1 %."