Thanks for the additional views. It almost appears as if there could be something other than the stand mounted in the hole on the aft section of the model; if the data plate was lost, it's possible that the exhaust nozzle of the model may have gone missing as well.
I'm leaning towards the views of Bill Rose, Moonbat, and Scott - From everything that I've heard and seen, this very well may be one of the final Isinglass configurations. I believe, based on other models that I have seen over the years, that this particular item probably sat in someone's secure office at an agency or a facility many, many years ago. 43 years after the project was "cancelled", I'd expect more gems related to that project to start showing up......