Cobra Rotor adapter bracket - Rotor specs needed

[witt19]

Hey all, i'm currently in the process of making a adapter for running r33 gts-t calipers with 13" cobra rotors. My question is, does anyone know what the offset of the rotors themselves are? I know with vr4 brake upgrade, the rotor offset requires a 15mm spacer for the adapter, which is taken care of by the thickness of the adapting bracket. I need to know the same information so i can make the correct dimensions for the adapter for the cobra bracket.

Any clues?