I think that little Aisin one is cute and more suitable for like a 1.5. Maybe put one on each bank of a 2.5.
There are SC roots kits for Subies.
And the inevitable How-To forums.
But all-in-all I suspect there's a reason so few people do it this way. I think if you want boost you just buy an STi motor and plumb the turbo to your own liking.