His brother, Evan, said that no official cause of death had been determined but that he had probably had a heart attack.
Throughout his career, Mr. McGlinn breathed the intoxicating air of the early Broadway musical, with special attention lavished on what are known as the Princess Musicals — giddy, innocent confections devised by Jerome Kern, with assistance from P. G. Wodehouse and Guy Bolton, in the first two decades of the 20th century at the Princess Theater.
Working backward through time, he pared away accretions to original scores, returned to original orchestrations, reinstated lost songs and, in concerts and recordings, exposed audiences to the primal versions of musicals that had been roughly treated over the years. His most ambitious reclamation effort was Show Boat, by Kern and Oscar Hammerstein 2d, which he restored to its original length of nearly four hours. Among other changes, he reinstated two songs whose scores had languished for decades in a Warner Brothers warehouse in Secaucus, N.J.
“He drew tremendous attention to early musicals that were swiftly becoming lost or forgotten, and brought them to the notice of a new generation,” Miles Kreuger, president of the Institute of the American Musical, said. “He recorded many songs for the very first time.”
John Alexander McGlinn 3rd was born in Bryn Mawr, Pa., and grew up in nearby Gladwyne. A self-taught pianist, he studied music theory and composition at Northwestern University, from which he graduated in 1976.
Mr. McGlinn moved to New York and, caught up in the renewed interest in American songs performed in period style, recorded “Songs of New York” for Book-of-the-Month Records.
For the Houston Grand Opera, Mr. McGlinn embarked on what would become a thorough overhaul of Show Boat, which had been revised, and shortened, multiple times since its premiere in 1927. Consulting archives at the Rodgers & Hammerstein office and the London offices of Chappell Music, he pieced together a partly restored version that, after touring the United States, ran briefly on Broadway in 1983.
