R32 GTSt disc diam is 280mm, new thickness is 30mm
R32 GTR disc diam is 296mm, new thickness is 32mm
I looked at some GTR cals today and they appeared identical to the GTSt type to me, BUT that was only a visual comparison, so no way I'm sure on this. Whether GTR discs and cals will bolt up easily to a GTSt I can't say, but would be surprised if more mods were'nt required.