Thank you for the recommendation and insight jffr and Ieea. In the end I may take your advice to wait for an original gauge to show-up on eBay (there is one now with a starting bid of $200), but for now I am going to try my skills on getting a Fiat Veglia gauge to work. I am waiting for one to arrive that was only $20 (incl. shipping), that supposedly worked when pulled from its Fiat 124 Spider donor.
My plan is to test the gauge for function and temperature calibration with my Ford sender unit. Then I will try the delicate surgery of swapping the Fiat internals to my original gauge. I will try my best to document this work and let The Forum know the result.
I will also keep my eye open for an original Pantera gauge on eBay