No updates as such at the moment as the build hasn't moved on much from when I saw it, but I did manage to get hold of some more specific details of the engine. I'll be collating as much information as I can thoughout the build so there is a complete specification list when the car is finished.
Engine:
Impreza WRC block.
Impreza WRC cams.
Arrow crank.
Arrow rods.
Omega pistons (running at 10.1 compression).
Dry sumped.
Garrett GT35R V-band turbocharger (with FiA mandated 45mm restrictor).
Modified Impreza S9 WRC inconel exhaust.
548 BHP and 554 Ft. Lbs. in the 5000 - 6500 RPM range.
Transmission:
Tilton Impreza WRC pattern one piece Billet steel flywheel.
Twin plate cerametallic clutch.
Hewland Impreza WRC six speed manual gearbox.
Impreza S5 WRC rear differential.
I also asked Kevin about the radiator setup as I noticed that the US rallycross Impreza's use a (rather cool looking) ducting setup running from the rear quarter glass:
Sadly it seems that such a design would fail to comply with FiA build regulations though, so the intakes for the rear radiators will be located in the rear doors themselves.