The original theme song had a calypso beat and different lyrics. Incidentally, the original was penned by music legend John Williams. (The Creator/Producer) Sherwood Schwartz himself sang the theme song,
The original lyrics also describe several new characters that "Gilligan's Island" fans may not be familiar with. "Two secretaries from U.S.A.," the lyrics say, "'they on the Minnow this lovely day. A high school teacher is next aboard, all taking trip that they cannot afford." The lyrics do describe the Millionaire and his Wife, at any rate, and Gilligan and the Skipper are still there piloting the S.S. Minnow. There is no mention of Ginger the movie star, the Professor, or the farm girl Mary Ann.
The calypso song was used for "Marooned," the original "Gilligan's Island" pilot, and it wouldn't be heard by the public until October 16, 1992
More about the "Others" in the Cast that were changed:
https://www.slashfilm.com/1643886/gilligans-island-unaired-pilot-marooned/
Watch it in its entirety:
LA Times original Review - “ ‘Gilligan’s Island’ is a television series that never should have reached the air this season, or any other season.”
The New York Times was equally uncharitable: “ ‘Gilligan’s Island’ is quite possibly the most preposterous situation comedy of the season.”
Turner TV had the negative and brought it back ...
https://www.latimes.com/archives/la-xpm-1992-10-11-tv-154-story.html