Matt Walters, Matt Roper, Noah Diamond, and Seth Shelden are Zeppo, Chico, Groucho, and Harpo in a new revival of the Marx Brothers’ lost musical, “I’ll Say She Is.” Photograph by Mark X. Hopkins. Courtesy Gimme a Thrill Productions.

On a recent Saturday morning at the Pearl Studios, on Eighth Avenue, the most labyrinthine of all Broadway rehearsal halls, one of the most beautiful and endangered of all New York sounds suddenly materialized: the shatter and thunder of massed tap dancers on a wooden studio floor. The chorus line of a new show was working on a new-old number, and the dancers, instead of being all-of-a-kind, post-Fosse giraffes and gazelles, had the pixie faces and powerful thighs you would see on chorus lines from the nineteen-twenties and early thirties. “We wanted that kind of casting-call variety of types,” one of the directors said. “We told the girls not to do any work outs for the duration of the run. They shouldn’t have muscle tone. Just muscles.”

The need to have a group of dancers who resemble their own great-grandmothers comes about because the enterprise at hand is a revival of a twenties musical—and not even so much a revival, in the manner of the current “Shuffle Along,” as a full-scale, quixotic reconstruction, as improbable in ambition as the remaking of a Giganotosaurus skeleton from two shin bones and a tooth worn down by time, of the lost 1924 Marx Brothers musical “I’ll Say She Is.” Having opened in May of that high Jazz Age year at the Moorish Revival-style Casino Theatre, to rapturous reviews—one in particular, from Alexander Woollcott, more or less made the brothers’ reputation—the show closed the following February (a fine run for the time), never to be seen onstage again. One of the legendary late débuts of American theatrical history (the Marxes were well into their thirties when they finally escaped vaudeville for the stage), “I’ll Say She Is!” contained—nice chance to use the tendentious form of “arguably” here—arguably the most influential of all twentieth-century comic sketches, the legendary “Napoleon” scene that, more than any other five minutes in comedy, began the line of absurdist pop humor that continued on directly from the Marxes to Ernie Kovacs and right through to Monty Python.

To call the musical “lost” implies that someone was looking for it. In truth, it was simply gone—gone into the same netherworld of fading programs and yellowing clippings that most other revues of the time have fallen into. Now it’s here again. The Quixotes who fought for its return are the New York writer and performer Noah Diamond and his wife, the director Amanda Sisk, accompanied by a gang of twenty- and thirty-something friends. Their windmill, for much of the past ten years, has been a full-scale stage revival, which they’ve now finally achieved, at the Connelly Theatre, on the Lower East Side, where the will open at last on Thursday evening. (For all the clichés of ascent from the tenements, that neighborhood was not really the Marxes’ haunt; they were strictly Yorkville boys, raised around 93rd and Lexington.)

The hunt to find “I’ll Say She Is” began when Diamond, as an adolescent growing up in the New York suburbs in the nineteen-eighties, fell in love, as awkward young men often do, with the mystique of the Marxes. “I was one of those kids,” he says. “Groucho was my God.” His worship extended to trying to woo girls with borrowed Grouchoisms. “Your eyes shine like the pants of my blue serge suit,” he would say to some winsome Thelma Todd of the eighties, a doubly baffling come-on: the girl had no idea what a blue serge suit was, and neither did he.

Infatuation ripened into impersonation. Diamond’s Groucho, which he has worked on for almost thirty years and showcased on many occasions, is genuinely uncanny, capturing the subtle truth that Groucho’s voice, far from being a machine-gun wise guy’s, is essentially soft and grainy, rising to its trebly heights only in feigned indignation. (Diamond also makes the interesting point that, while the original Groucho had to project his lines unamplified into a large Broadway theatre, we are now so used to hearing Groucho exclusively through his miked performances, in movies and on television, that he only sounds fully “Groucho” when miked onstage.)

“ ‘I’ll Say She Is’ always haunted me,” Diamond says. The Marx Brothers’ two other Broadway hits—the George Kaufman-penned “The Cocoanuts” and “Animal Crackers”—were adapted into movies while they were still running onstage. “I’ll Say She Is,” though, in its day, at least as famous as the other two, had just passed away: as a revue it had no appealing afterlife for other performers, and, so far as anyone knew, no script of any kind had survived; its score, written largely by the cartoonist and humorist Will B. Johnstone, with music by his brother Tom, had never been recorded.

The dinosaur shinbone, in this case, was a typescript of Johnstone’s, a well-thumbed old draft outlining the show’s scenes. It was not really a script but more what a contemporary screenwriter would call a treatment. Diamond also knew that a short film made by the Marxes in the early thirties, as a kind of teaser for their feature “Monkey Business,” reproduced, in only very slightly different form, one of the lost musical’s key scenes. Another key scene, the Napoleon sketch, survived as well, in a script that had remained in Groucho’s archives. There was also a single, soiled molar to build around: a version of the Napoleon scene that had, improbably, been made into a rather mediocre episode in a long-forgotten, cheaply made cartoon special in 1970, with the very elderly Groucho supplying his lines and Hans Conried doing the other brother’s voices. A disappointing delivery, but a delivery all the same. (Diamond also points out that the show’s revival is as much as product of YouTube as of Broadway—only in the digital age did the whole archive of the past become available.)

The rest of the dinosaur had to be recreated, so to speak, from imaginative reconstruction. Quote by quote, line-by-line, and joke-by-joke, Diamond reassembled the script, or a reasonable facsimile thereof. Note by note and syllable by syllable, he reassembled the score, recycling music from other Johnstone scores and melding it with that of his own lyrical mind. The musical’s songs, which were famously mediocre—Groucho himself called the score “the most undistinguished one that ever bruised the eardrums of a Broadway audience”—had nonetheless to be re-created, reconstructed, and quietly improved. The pre-jazz operetta, slightly ragtime music was, Diamond knew, essential to the effect: without that roistering tone, however dated, one can’t register the Marxes’ seismographic surprises.

Becoming the Marx Brothers, meanwhile, is more operatically ambitious than it might seem. The skills picked up during a decade on the vaudeville road have to be re-created, painstakingly, in months. In need of brothers to join him in the pursuit, Diamond enlisted Seth Shelden, a brilliant young intellectual-property lawyer who was just returning from a Fulbright fellowship in Latvia. Improbable though it seems, Shelden’s secret ambition had always been to become Harpo Marx. “There was something about Harpo that turned me on—not so much his mime but his wildness,” he said. Shelden not only mastered the art of chasing blondes, blowing klaxons, and making the Gookie—the legendary puffed-cheek and lolling-tongue face that Harpo copied from a cigar roller in Yorkville—but also had to learn how to play the harp. A young British actor named Matt Roper, enlisted to play Chico, had to learn how to reproduce a fiendishly singular accent—not an Italian accent but a New York Italian-émigré accent as rendered in caricature by an émigré New York Jew—as well as how to play “trick” piano, in the distinctive Chico style, with the left hand lolling and the right hand shooting the keys and kittening. (According to legend, Chico’s instructor in this art was one-handed.) For Zeppo, Diamond and Zisk chose an old friend of Diamond’s named Matt Walters, who is at once extremely handsome and oddly nondescript, in the Zeppo manner.