On the GT-R UK Forum a member posted up some pictures and thoughts about shaftless throttles for an RB26
The increase in airflow for a 45mm is equivalent to running a 48mm throttle - but as the GTR one is a 10mm shaft, rather than a more usual 8mm shaft, it could be more of a gain. at 48mm you're talking a 15% increase in cross sectional area. But, because the throttle diameter is the same, you're not loosing out on torque - Plus everything else would fit as normal.
The price for three DCOE bodies is roughly £450. These should be cheaper as the machining is much simpler (no injector hole, or idle screws etc).