Sorry for the delayed response, we've been super busy!
The fuel rail adapter is being fabricated as we speak. It looks pretty simple, should only add maybe $10-15 to the cost of the manifold. We should have it done in a few days.
This manifold will drop in on the USDM WRX. Removing the TGV's will cause a CEL. This CEL can be deleted (ignored) with systems like the Cobb Access Port. There are definite gains by going with this manifold - the manifold becomes the single largest restriction on really high horsepower cars. We recommend a retune for use with this manifold though it is not absolutely necessary for most cars.