The 2005 - 2006 Legacy GT is the only car that used the Dual Mass Flywheel. The cranks are all the same, so don't worry about which engine you have in the car. Simply put, you do not want to use the Dual Mass flywheel (very expensive), so you just need a 2006+ WRX flywheel, and the clutch that matches - 2006+ WRX.
The rule of thumb is that Transmission determines the clutch that you need. The clutch determines the flywheel that you need.
If you are still using the Dual Mass Flywheel, you will most likely have to switch out the flywheel bolts for those that also go with the 2006 WRX flywheel as well.
Good luck with your project.