The number of three "Shelby Panteras" comes from journalist reporting back around 1982.
When Shelby was at Chrysler with Ioccoca running it, Ioccoca was interested in offering an Italian exotic very much like "the Duece" did at Ford in 1962. That resulted in the Ferrari debockle.
Shelby's facility in California was called the "Skunkworks". There is where he had his people create the Shelby Chrysler products.
As far as I know, there were three 82 Panteras seen there by the press. I heard of one that Ioccoca had Shelby install a small block Dodge 318 or 340 in for testing.
The story as presented to the public by the press was that only one was modified.
That project never developed into an Italian exotic product for Chrysler but must have been involved with Chrysler's decision to buy Lamborghini and develop the Viper? The 91 or 92 Diablo clearly shows a Chrysler VIN tag on it and Leedo himself introduced it to the press.
In some discussion with Kirk Evans here on this forum, who was/is Amerisport, he stated that he had something of the order of a dozed, i.e., 12 Panteras with invoices shown as shipped to Shelby that he was contracted with to "legalize in the US".
Kirk had the job of "US legalizing" the cars, which were not DOT certified at the time. So the point of this post by me is to question the quantity of "Shelby Panteras" as only being 3?
One of our members here, BelgiumBarry, had a "Euro Pantera" that was originally "invoiced" to Shelby.
In discussing that here on this forum, he knew little about that subject and I believe that thread is where Evans chimed in about what he knew.
Maybe someone smarter then me can find that thread here? It might be of interest to you if in fact you hadn't know about it to begin with?