Ain't this forum great? Joecj76 has one of these rare birds.
I got looking through my '69 Owners Manual and came across two references to this step. Neither one showed any pictures of it, though.
On page 103 of the manual it states, "The auxiliary step extension (optional) can be placed into position by unfolding the wings of the step extension and inserting the square bars into the holes provided in the front of the fold-away step. Do not travel with auxiliary step inserted in fold-away step. Place the auxiliary step in the storage bracket provided under the trailer, forward of the main step."
So, either the one I've seen was a homemade replica, or had been modified to remove the folding wings feature. Plus, with this step, apparently, one also got an under-the-trailer bracket in which to store the thing.
I'll be anxious to see joecj76's photos, as now I'm thinking I'd like a lower step, too.