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Are you sure you have the correct lines. The 6 and 4 brembo ends look like this
So your caliper bolts are 12mm and so are the brembo. Whats the problem then? Just make sure you get the right bolts for the brembo. PBR and brembo are different pitch. Part No for the rear is GM-92139080. The size is 12mm x 1.75 pitch . 45mm in length. Fronts should be the same. When you pull one of your front bolts out out measure the length.