I have a '71 with the extra step.
Here are some photos that may help or confuse you
The sides of the step are hinges that rotate all the way around. There is a bracket under the trailer with slots for the step poles to slide into and a bolt to hold it in place.
The step is removed and the sides rotate all the way around before sliding in place on the built- step.
The pictures show the step in place, removed and set on the ground. Next the sides up, but the step is upside down still. Then the bracket under the trailer. Finally the step with the sides rotated in place.