And since an EJ20T puts out 150kw and EJ22 only puts out 100kw (or thereabouts) you can still put one in since they have less than 120% more power than the EJ20T - in fact they only have 66% of the power

Even without the Forester having a turbo motor as an option the EJ22 would still be allowed since (I assume) it doesn't put out more than 120% of the power of an EJ20. You may run into trouble with the emissions though unless the EJ22 will run on the standard Foz ECU ??