Grand Funk Railroad’s hit version of "Some Kind of Wonderful" comes from the 1970s.
Grand Funk Railroad recorded the song for its 1974 album All the Girls in the World Beware!!! The band’s single was released in December 1974, placing it firmly in the seventies. It became one of Grand Funk’s best-known late-period hits and helped keep the group prominent on American rock radio.
The song was not originally written by Grand Funk Railroad. Canadian-American musician John Ellison wrote it, and his group, the Soul Brothers Six, first recorded it in 1967. Grand Funk’s heavier rock interpretation transformed the earlier rhythm-and-blues song into a major album-rock and pop-rock success.
A common mix-up comes from the song’s earlier recordings. The original Soul Brothers Six version belongs to the 1960s, but the version named in this question is specifically Grand Funk Railroad’s. That recording dates to 1974, so “Seventies” is the single canonical decade answer.