The VL standard auto non trb has 3.45.
R31 Skyline auto has 3.9, and manuals have 3.7.
The gears are dirt cheap from wreckers, just have to get them onto a carrier for your diff.
All I'm gonna tell you is that with 3.7, 3.9, or 4.11, your gonna have a hard time getting the thing off the line... should be good fun mate