My brother Steve sent these two pictures, which were taken on July 4, 1975. The original images' caption (not shown here) says, "Marxhausen Seward Fourth of July Parade float. Old St. John Lutheran Church in the background."
Steve says that the bottom picture shows the front of the float being held by Karl Marxhausen (in the foreground) and Reinhold Marxhausen (in the background). The back of the float was held by Paul and Dorris Marxhausen (son and mother) and some friends, but they are not seen in these pictures.
Karl Marxhausen, in his own blog, added this information:
Dad used hula hoops for the four corners. With a walker in each hoop. He created a fish line grid, to which inflated ballons were secured. The rectangular float could be elevated by the front and back walkers moving to the middle, creating a 20 high arch.