The WRC manifold is just the inner part of the inlet and a fuel rail. The outer cover is all as per either 2wd (limited to around 430-450bhp), the 4x4 one (limited to around 450-470bhp) or the EECIV one (limited to around 500bhp). This is all down to the elbow design, and the RS500 one is superior for flow.

Personally, I think your choice should only boil down to how much power you want to achieve, otherwise it is pointless changing it.