Legit American-lit marathon “Gatz” is set for a return run this spring at Off Broadway’s Public Theater, where the show turned into an unlikely crowd magnet last year.

Elevator Repair Service’s 6 1/2-hour stage version of “The Great Gatsby,” which centers on an office worker who becomes engrossed in reading the F. Scott Fitzgerald novel, encompasses a verbatim reading of the entire book. Scott Shepherd will reprise his role as the office worker.

Despite the arty production’s hefty running time, the show — which has toured the country — became a notable success at the Public and sold out its run even before it opened.

This spring “Gatz” will be back for a seven-week engagement that runs March 14-May 6. Encore of the show replaces the previously skedded preem of Nathan Englander’s play “The Twenty-Seventh Man,” now set to open in November 2012. Show was pushed back due to a scheduling conflict among the collaborators, according to the Public.

Elevator Repair Service’s recent version of “The Sun Also Rises” played Off Broadway’s New York Theater Workshop earlier this year.