Even if there are Kenner Ecto-Headphones instructions out there somewhere I have come up with a workable solution. While creating the potential instruction page I was looking at the back of its box. In the lower hand corner the box has an Assembly area. I cropped an existing photo of the box I took within the last two years.
This photo can serve as a more detailed visual for how to use Ecto-Headphones and assemble it. A scan of two The Real Ghostbusters decals are also included.