The 2wd manifold suffers from NVH problems, hence why it has to have a turbo damper on it. However, it is very efficient given that it is on a 204bhp car, as it doesn't actually become restrictive until 580bhp .

To overcome the NVH issues, Ford redesigned the manifold and this was then fitted on all the 4x4 cars. However, due to it not needing a turbo damper, the mounting point for this was no longer necessary, so was deleted from the 4x4 heads. Unfortunately, although the design eliminated the NVH problems, it lowered the power out-put of the restriction point to well under 500bhp (YUM's car did 466bhp with one, which is as much as I would want to push one to). Despite this, low down torque is alleged to be slightly improved due to the smaller internal diameters of the headers giving better gas speed to the turbo.

Now you can probably guess from the above as to why you see them swapped between head / transmission types - it all depends on what numbers you are chasing .

Cast manifolds seem to have a greater durability than their tubular brothers, but the tubular ones can be made to give very exacting power characteristics and it's a lot easier to get an equal length with this design in a particularly confined space compared to a cast item. To have one cast would actually be more expensive for a one off compared to a tubular one, but once the mould has been made, they can be banged out far more cheaply than a hand-made tubular item.