Cobb ftw. Perfect fitment, great quality. But what you really need is just a bellmouth DP. Its been explained on here before. But most "divorced wastegates" arent truely divorced, just a plate in the middle of the downpipe which causes problems with fitment sometimes. You need to shave or cut the piece that seperates the gas flow for proper fitment. I believe on Perrins site they actual make mention of it on their DP.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX