Make sure you get GTS caliper bolts
(M12 x 80 x 1.5) as replacements, rather than M12 x 70's
Use High Grade 10.9 instead of 8.8 bolts for fitting Porsche Brembo Calipers the the steering knuckle.
Part number 900.067.268.02 or 900.067.432.01
Be very careful not to damage the head, and if possible, renew the bolts every time you undo them. Grease them before inserting.
If you screw up the head a real misery starts. They must come out to remove the caliper. A last resort would be these undo tools: