Maybe this helps.
TO put Brembo's on any pre 08 Impreza/WRX -
-You accommodate the different mounting point w/ either the brackets or 06/07 back plate.
-You accommodate the larger park brake drum by either the thicker ebrake shoes or adaptor rotor.
The adaptor rotor is more than a cheap 04 STi rotor - but is much easier to install.
The ebrake shoe is perhaps cheaper overall - but not all STi rotors seal the park brake correctly.
I think both paths are pretty equal overall - neither are perfect but both work well enough to like them.