Here in New York, in its fourth incarnation since it originally played on Broadway in 1957, Meredith Willson’s slice of musical Americana does not fail to please. Willson wrote book, lyrics and music, and collaborated on the story with Franklin Lacey. Helmed by director Jerry Zaks, whose pedigree includes a super production of “Hello, Dolly” some seasons back, the musical gives audiences a masterful coordination of performers, sets, costumes, and music. Musical Middle America The setting is the fictitious River City, Iowa, in the more innocent times of the pre-1920s. The show opens in a sumptuous train car of the time, trimmed with rich mahogany and luscious green velvet, courtesy of veteran designer Santo Loquasto, who also created the vivid costumes. Here a group of traveling salesmen, led by Remy Auberjonois, jiggle in time to the rhythmic beat of the train’s rattle. The men’s talk turns to mention of the …