I think a evo 8 or 9 with a built 4g63 would be better suited for you.
The things you like about the Suby
-Sound: with a 600whp subaru you will need equal length or twinscroll, so the boxer sound will most likely be gone.
-Refinement/Look: they both look somewhat similar :P
-Transmission: you would probably have to put straight cut in either.
And for the price it would be way easier/cheaper to achieve your goals with a 4g63.