Black Sabbath with Jo Jo Gunne and Gentle Giant were scheduled to perform at the Minneapolis Armory on August 28, 1972, presented by Howard Stein and Owen Husney.  This was Black Sabbath’s  “Volume 4” Tour:

Touring Personnel

• Ozzy Osbourne – Vocals
• Tony Iommi – Guitar
• Geezer Butler – Bass
• Bill Ward – Drums

A Gentle Giant fan site says:

At one time, they had planned to open for Yes on the West Coast from Aug. 15 through Aug. 20, but it turned out their very first North American gigs were on a U.S. tour with Black Sabbath later in the month, an odd mismatch to be sure. They had shared a stage with this band on occasion before but, on this tour, the band did not always go over well with the Sabbath crowd, giving Giant some unpleasant early experiences in America. Out of necessity, they had to sometimes play in a heavier style and “rock out” more, in order to get through the gigs. Even though the band members do recall having audience trouble at times on this tour, Gary Green also remembers Giant being treated well by Sabbath’s lead singer, Ozzy Osbourne.

Gentle Giant ad, August-September 1972

The Minneapolis show was rescheduled to October 5, 1972, because Ozzy Osbourne had lost his voice.  Still looking for documentation that the October 5 event took place.  Gentle Giant was added to the already scheduled show on September 23 with Yes and the Eagles.