Ah yes, but that wasn’t the question. The master cylinder on the V8 Calais will be the same bore diameter as the HSV master that the brakes were engineered to be used with and there will not be any change required for brake bias or ABS.
True that certification wasn’t the (direct) question but last I played with brake systems was well before the advent of ABS.
As I understood it back then, the master cylinder bore diameter influences the volume of fluid pushed into the front and read lines which had to marry up with caliper piston movement (volume). The mechanical proportioning valve used two internal pistons and springs within the master cylinder to apportion different line pressure front and back. It was the spring tension that provided the magic that made such happen.
Today, brake bias isn’t solely handled by the mechanical proportioning valve in the master cylinder. Heck, has some makes don’t even have a mechanical proportioning valve any longer as it’s all handled by ABS/EBD. In the VF, brake bias is enhanced/controlled by ABS/EBD unit so it’s a potential programming issue that needs to be considered along with fluid volumes.
So just comparing a master cylinder bore diameter across model variant without looking at other mechanical issues along with the ABS/EBD/ESC calibration side of the equation in our modern cars almost certainly will not be enough.
I’d think it’s a small cost to get a certificate from an engineer and ensure compliance, but hay, it’s not my car and it’s not my insurance policy on the line so what do I know
