Rocky, a few people (very few!) have adapted rear pads from the Porsche 914 to stock Pantera rear calipers. Then 914 rear pads can be had in several compounds from places like PelicanParts.com. Virtually no one makes performance pads for the Peugeot 205- which is where our stock rear calipers were sourced.
Finding the right compound for your driving use & style will be a try-it-and-see exercise that may cost more than changing to real rear calipers & vented rotors. And the stock Pantera brake plumbing biases more pressure to the rear while the excellent fronts are mostly along for the ride. This is exactly backward to all other cars on the road, for reasons known only to Ford engineering. To do what you want WILL require some parts swapping.... or going slower.
On the 914, their rear pads sort-of work OK but that car can be 1000 lbs lighter than your Pantera. So don't expect miracles: you need new pads to work better without wearing out the rotors too fast; normally you get one or the other. I would CALL Porterfield in CA on the phone and discuss options.