Earlier R53 cars had an M12 bolt, later cars have an M14 bolt but that will make no difference to fitting the discs.
The two bolts that hold the caliper on are the same.
As mentioned..... The R56 STANDARD brake kit is the same as the R53
JCW brake kit but its not painted red and badged as a
JCW brake.
So the R53 and R56 have interchangable brakes.
Like snowie says, he has an R53
JCW GP with R56
JCW Drilled and Slotted Rotors so they do work.
Scott