It wasn't that tough to find after all. Conveniently in a Prism speed bag marked Aerostar, LOL
The inner stand - off measures slightly over 2mm and the Upper spreader is about 4.5mm (approximately 3/16") and measures 19 5/16 " long. BTW there is a sleeve similar to a shink wrap at each end of the upper spreader to keep it in the fittings.
That's about the best I can do and we must consider that the calipers I'm using are from the turn of the century (20th, ie) that I inherited from my grandfather about 45 years ago. I had to transfer over the dimensions to a tape measure as the calipers are in inch and you can't read the markings anymore.
With my +2.75 reading glasses I can assure you that these measurements are close