Could be wrong here, but ....
I put one on my previous gen3 legacy B4 and although it worked fine (the bov) the car ran like shite when stopped at lights etc, and often cut out. I'm sure your aware of this.something about the air being already metered for and then all of a sudden it's vented and the ECU is still expecting the air and adds the appropriate amount of fuel for said air, engine runs rich for brief moment and can cutout.
That being said, I did have a adaptor plate machined up for it , it wasn't the most expensive bov, but if I can find it(it's here somewhere) your more than welcome to it for free to experiment with it.
Other than that you probably need a variable adjustable one to minimise that problem.