1998 Subaru legacy GT

Group-A pulleys
Group-A pitch mount
Brakes, pads, lines, fluid, new OEM sized rotors

First why are 2.5 RS's in G stock but LGT's are in H-Stock?....
Second the SS lines take me out of Stock right? I think I would be in ST
Can the sig lighter ash try stuff like that be removed?
I know my Group-A pitch mount puts me out of ST so I'm going to replace it with a Group-N one.
04 STi rims with 225 tires would be perfect for ST right?
If I red correctly I could have Borla knock of headers with just about any cat-back BUT cats have to be stock?

Thanks