Chuck, my spacer recommendation is based on achieving 20mm inset for both front and rear tires. The inexpensive one piece wheels are produced in a bunch of offsets for modern cars. TSW has some of the smallest offsets out there, thus they have wheels that can be adapted for Panteras using typically thin spacers.
The front spacer is only 4mm, definitely won't need longer studs. The rear spacer is 7mm, it may need longer studs, it may not. Depends upon how much thread engagement remains … which depends upon how thick the wheel flanges are. Won't know until you buy them.
You could opt for 24mm inset, the front would need no spacer at all, the rear only 3mm. Try that first, if you decide you don't like the look of the wheels & tires inset that much, move the spacers to the front, and buy another pair of 6mm spacers for the rear.
If you want to see the wheels on "a car" (obviously not a Pantera) at the TSW website select an Audi TT.