Okay so I just looked up again about the twin scroll turbos to find out why I thought they wouldn't work. The twin scroll case splits the exhaust from each port (head?), so there would need to be some exhaust mods to make it work in the WRX. To me that was a non-starter since I'm trying to keep as much stock as possible to keep costs down. Plus, doesn't that change the character of the boxer rumble? Maybe not if the pipes are built right, but still more expensive ...