R34 GTR N1 Turbos have the same specs as HKS GT-SS, as in the Compressor Wheel and Turbine Wheel.
Previous owner would have just upgraded the actuators to HKS to replicate the HKS GT-SS to save from buying 2 whole new Turbos... IMO.
Both these Turbos are pretty much the equivalent to the Garrett -7's Turbos.
I believe Garrett make all Turbos, aftermarket tuning houses just put their name / badge on it and give it a different name