I have owned five Panteras and four of them had the stock coolant bypass plate along with the appropriate thermostat with a hat that plugs the bypass hole when the engine is hot.
The Pantera that I am currently driving came with a bypass restrictor plate and it requires a Windsor thermostat (no hat). I have put about 1,000 miles on it and it never overheats. In the morning the car warms up just like my other Panteras. I live in Southern California and it is rarely cold here. I have been using a Stant thermostat and I am in the process of replacing it with a Flowcooler high volume thermostat. It is also getting a Flowcooler water pump in place of a traditional water pump. It has a shrouded aluminum radiator from Pantera Performance Center that is made by Ron Davis Racing Products.
I am wondering what is down side to continuing with the coolant bypass restrictor plate that came with the car. It seems the primary benefit of the stock bypass plate is that the engine warms up faster but this car gets warm as fast as my other Panteras.