One of the biggest issues with the Greddy intake manifold kit or others like it is that the IACV flange is suited for the Series 1 or 2 RB25DET.  If you have a R34 or WNC34 with a RB25DET NEO Engine then you have a completely different Idle Air Control Valve (IACV) & if you wanted to use these forward facing plenums you would heave to buy the old series 1 or 2 one & re-wire that in.