Without knowing what manifold (and more importantly the fuel rail) you're talking about anyone that gives an answer will just be guessing.
With that said ... the Greddy manifold doesn't require an aftermarket fuel rail and if you're talking about the HKS rail, then yes you need high impedance top feed injectors. However, you can use low impedance injectors if you use a resistor pack.
i wanted to buy the greddy fuel rail and high impedance injectors