The cast of one of basic cable’s funniest shows, “It’s Always Sunny in Philadelphia,” is taking to the road in September to perform the show’s mock rock opera, “The Nightman Cometh,” Paste Magazine reported today. The six-date tour will play three dates in the Northeast, beginning September 15, and and end on September 25 after three dates on the West Coast. The popular television show, which is on FX, is slated to run through 2011.