One Man, Two Guvnors, Four Musicians: How a Group of American Rockers Learned to Be Convincingly British

Skiffle instruments include washboard, tea chests and car horns

“You get to feel the energy of the actors, the audience, the set pieces, all of the design that went into the show,” he said, “and it directly influences the way you behave, in the same way it does an actor.”

He and the rest of the Craze have striven, despite the matching suits, to “be a little unpolished.” Although Mr. Rosen called the band’s sound, “by today’s standards, a little tame,” skiffle is raw compared to the Disneyfied scores of most Broadway musicals.

“The important thing is to get the detail right, to make it feel authentic, and not forget that we’ve gotta have fun doing it,” Mr. Olding said, as Mr. Rosen gave his upright bass a twirl.

“He wants to spin his bass,” said Mr. Olding. “That’s new for us. We don’t spin the bass in London. He’s all over spinning that bass.”

By Friday, if all goes according to plan, nearly every such Americanism will be sanded away, allowing the play’s uniquely British silliness to shine through.