Hi Sean,
It is the official 3 Port Boost Solenoid, as fitted to the WR1, I paid £190 from Subaru(probably got ripped off) Please see the URL below for a pic. The part number is 16102AA013, there's no fitting instructions, sure there will be some where on the net.
http://www.btinternet.com/~paulj.ewing/SpecC/3PBS.jpg
Prefer to meet up than post.
Cheers,
Paul