Sounds like a boxer rumble to me....
FYI its confirmed there will be a turbocharged variant of this platform. Subaru is doing development on a low compression engine version and released at TAS a 1.8 turbo version of the BRZ engine. Its not surprising, the transmission should support 300whp of abuse. Sound/Power doesnt matter...this car makes 200hp at the crank
Unequal vs Equal length in relevance to power isn't going to be significant no matter which way you cut it. Personally.. if I'm going to do heavy modifications, I'd go unequal length. By the judge of this video..its been done.