If memory serves me correctly 94-98 GTs Master Cylinder Bore size is 11/16th of an inch...
Without knowing the pedal ratio, and assuming 100 pounds of foot pressue, I would ballpark 1,100PSI. But don't
quote me on it..
You don't need to know the operating pressure of the master cylinder to build a pressure bleeder. When you pressure bleed the brakes, it will be an open system. Hook up your air compressor to it and voila, it's done.