IMO The red manifolds is just an Sti thing to distinguish them from the WRX's. WRX RA's wouldn't have had a red manifold.
Yours must be either a paint job, a manifold change or maybe an engine upgrade.
The car was bought in Bristol as a fresh import. The rest of the car is as a WRX V-Ltd should be, but it does have STi 6 cosmetics, including rear wing, fog light covers and front brace. I would have thought painting the manifold red would have taken quite a lot of effort (especially as lots of the paint has flaked off in typical fashion!) and the intercooler is normal WRX black...
I wonder if this could have been a factory option, as it seems like a lot of effort to change this and then not bother to change the intercooler? Standard turbo is fitted; I'll see if I can find any more STi parts in the engine bay!