Old thread is gone now, it looks like. I decided to take my car in a slightly different, and easier, direction with the motor setup.
Problems with the previous plan: Few people have EJ22T swaps, and no one has done what I was doing before. IE EJ22T/EJ25 Hybrid, STi Intake, so on and so forth.
The key issue is the fitment of the stock WRX exhaust components with the 2.5 RS heads, they dont clear them. So, I have a new plan.
As soon as my return gets deposited, hopefully this week, I will be ordering an Version 3 STi motor and transmission, the EJ20K. The engine management has not changed, Megasquirt 2. The swap will be completed much sooner this time, as I don't have to track down and mix/match parts. In addition, some of the other stuff I collected will be used on this build as well, like my exhaust. Hopefully though, she will be running here soon.
This also sets up future options for the car as well. The 20K's are rumored to have weak bottom end. The community seems pretty split down the middle about their reliability, but the point is that if the bottom ever lets go, that paves the way for the standard EJ20/EJ257 hybrid build. So either way, I think this is the best route. I get a beefier transmission with this setup too.