As Raj said I have one in my GTT, haven't had any issues with it. I track my car frequently and will consistently do 5 or more fast laps in a session without a cooldown and have not had any oveeheating issues with coolant or oil (mishimoto oil cooler too).
The radiator I have is the MMRAD-RHD-R33 which is their 33GTR unit and that was a direct fit with no modifications required.