the gtr rotors will not fit the gtt calipers.
i did a brake/rotor upgrade on my r34 n/a and i was going for dba slotted all round but i could only get the rear, so i had to rda and at the time they didnt make 310mm (gtt size) rotors, so i had to get the 324mm rotors, being the gtr ones.
we tried to fit the gtt calipers with the 324mm rotor but they did not fit at all, the caliper was rubbing against the rotor! so in the end we ended up machining the rotor down to 310mm.
hope this helps