I finally got to see McGuire on stage in The Young Man from Atlanta at the Goodman Theatre pre-Broadway in '97. Rip Torn and Shirley Knight were the leads. Knight and McGuire gave particularly powerful performances. Torn, of course, was a force of nature. He did a lot of schtick if I remember correctly, but was very charismatic and amazing to watch while he was doing it.
McGuire's wife Jeannie Carson had a TV series in the mid-50's and also played Jo March in a TV production of Little Women with a Richard Adler score. McGuire and Carson are delightful as Woody and Sharon on the '60 revival cast album of Finian's Rainbow.
I'm going to have to check out the South Pacific cast album CD tomorrow morning now that I know who actually sang that line.