[RichardJ]

>>each piston displaces brake fluid proportionately to their input,(some biasing takes place to prevent premature application of the front brakes and over application of the rear brakes.)<<

Neither is true. Brake pressure from the front and rear port are the same as long as there is no failure in the MC or any other part of the brake system.

>>You must keep the pin depressed while bleeding the brake system or your brake system warning light will turn on inside the dash cluster<<

Also not true. The pin is the end of the Metering Valve that is housed inside The Combination Valve. The Warning Switch operates independently from the Metering valve.
The Metering Valve HOLDS OFF fluid from the front brakes until line pressure reach's 40-60 lbs, depending on application. This holds off application of the front brakes until the rear brakes can begin to work and prevents nose-diving of the front end.
The Warning Switch Piston does not move if the pressure on both inlet ports is the same. 100lb on the front and 100lb on the rear port, the piston does not move. 600lb on the front port and 600lb on the rear port and the piston does not move. Sometimes there are springs on the front and rear of the switch piston so there can be some variation from equal pressure before switch contact is made and the light comes on.