When the car sits down front and back (when you brake) and it does not lock up, then it is balanced properly.
If the nose is diving under braking and the rear is "in the air", there is insufficient braking in the rear.
This is easier to see in an autocross car rather then a high speed track car because of the differences in speeds, but you are aiming for the same thing.
Oh, and for a performance car, you should be able to stand on the brakes, literally, and not be able to lock up the brakes.
This is how the street 65-6 Shelby GT350 brakes are set up. It is virtually impossible to lock the brakes up.
I doubt that the Pantera needs more then a 11.75 to 12" front rotor. Granted with the 17" rims those would look silly, but I don't think you need 14" front rims.
You can debate what the front thickness should be but 1.25" vented would probably be maximum. I happen to like that rotor.
A 67 Thunderbird rotor will substitute for the stock P on the P hub. It is 1.25" thick and 11.75" od. Of course you can go with a aftermarket composite also but they start to get pricy in this size, particularly plated/slotted/cross drilled.
You can open a can of worms with a 1.25" rotor. For one thing you need to micro cut the rotor on the car because of the mass. If it is the slightest out of balance, you won't be able to drive the car.
Probably 1" in the front, vented, is less problematic for a street car. The size of the pad, surface area, and the compound are important.
I like the Porterfield RS-4 compound. The R-4 is a race compound and you don't really want that on the street.
The rear is a different story rotor size wise.
I happen to think that the 68-9-0 Mustang front rotor is about right for the rear. 11.3"od x .81" thick vented. Too bad we can no longer get the original configuration, i.e., the current replacement rotor has the bearing hub cast into it. Probably a Willwood modular rotor in that size would be the substitute to use?
The 4 piston Willwoods front and rear is a great way to go. 6 piston in the front is nice but maybe a little to Lemans orientated then necessary?
Sure, because of the four mounting points on the stock P rear uprights, that opens the option of using the P original caliper as the parking brake. Actually a good idea.
This is probably how I will go on my Pantera.
I already have my GT350 set up this way with a 1-1/4" bore master and the setup is NICE!
The difference is the Shelby uses a 67 Tbird caliper. It is heavier and larger then the Willwood but it is what the vintage racers use on their cars and it is what "the factory race cars" used. It is very street-able since it came off of a production street car.
It is a brake system that was designed to stop a 6,000 pound car. It works on a 3,000 pound car twice as well.
Save the stock P front "proportioning valve", but have it mounted and bronzed and put it on the mantle. For this kind of a braking set up you need an adjustable proportioning valve for the rear.
It shouldn't be difficult to do. The Pantera unlike the Mangusta is inherently stable. It should just be a matter of getting the pressure just right?
I think the relative ease of "upgrading" brakes on this car as demonstrated by the number of vendors who have done it shows that.
I think the difficult and maybe dangerous part of this process is going to be building the adapter brackets for the car.
Maybe it is best to leave that to someone who can use his CAD program and, what is it now, a plasma cutter, to whittle them out of 1/2" plate?