I'm told that if you use DOHC EJ25 heads, it is a direct bolt on to your engine. Sensors, Intake manifold, everything. For the headgaskets, I'm pretty sure the normal EJ22 headgaskets won't line up with the ports on the heads. I know the SOHC heads don't. However luckily for us, the famous EJ22t heads have those same passages, so order the turbo legacy (91-94 I think) and all will be well. You will have to replace your timing belt with the DOHC for sure.