What are people talking about here? The phase II SOHC EJ25 heads use the exact same manifold bolt pattern as the USDM WRX's. Everything from '99 on is the same. If they are '98 or earlier WRX heads, then they use the same pattern as our '98 EJ25 DOHC heads. Coolant passages and head bolts, etc are totally a non-issue.
Regardless, this swap is a crap shoot. The smaller combustion chamber of the EJ205 heads (45cc vs 49cc of the SOHC EJ25) will bump your CR up to around 11:1, so gains will be had there. But the EJ205 heads flow 220cfm and the EJ25 SOHC heads flow 240cfm, and have substantially larger ports. Only if you replace the turbo camshafts with a pretty aggressive cam will you be able to make use of that extra CR.
Xephyr has a wagon with a similar setup, but he used the USDM DOHC EJ25 heads (which flow better than either of the above heads) on a phase II Ej25 block. He uses a 272 degree HKS cam meant for the WRX, and is getting about 5whp less than I am with my set up. But our powerbands are night and day different. He's got nothing below 4500rpm, and then it is like Vtec. It cranks all the way to 7000rpm.
My car comes on nearly 1000 rpms lower, and peaks at 5900rpm. But my torque curve is ridiculous. Over 200ft/lbs of torque from 3000-6400rpm when fuel cut hits. My power under the curve is substantially more than his...