[Rossba]

They look like PBR to me.
My XY came with Kelsey Hayes callipers but XY's also could come with PBR.
The Ford PBR and the HQ PBR calliper are the same but the HQ having a bigger piston than the Ford.
Howard at Race brakes recommended me to change mine in the XY to the PBR using the HQ calliper fitted in the Ford bracket as he makes a larger range of race pads for me to choose from. Because of HQ racing.

If yours are polished alloy then I would doubt they are HQ as I believe they were cast iron. You could be correct saying they are HZ, they could be the same caliper just updated to alloy in HZ.

Either way you have a calliper with the better slides and George builds a good car and you seem to know what you have so you are on a winner and enjoy your Cobra.

Ross