Just to share my experiences
Saw from website that some Japanese skyliners had changed the GTR34 brake cylinder (Part Number: 46010-AA320) to their GTTs and have great improvements, and I decided to give it a try.
I got the part from Nissan Japan directly during my trip to Japan last week, the price is 22,300 yen. FYI, I am using stock Nissan brake calipers with DBA4000 brake disc and ACRE light sport 0-500c brake pad.
I got it change today and the feeling is great! The brake power had been increased, not dramatically, but you can really feel that the brake is now more stiff and REAL. No need to step on the brake pedal as deep as before to provide the same braking power. I can feel the great difference expecially when I am going fast and downhill. I am 100% satisfied with the modification. No need to cut or wield or anything, just detach the old one and install the new one, that's it!
GTR34 brake cylinder
Original GTT brake cylinder
GTR34 vs GTT brake cylinder
GTR34 brake cylinder installed