So I guess i should swap in an 03 WRX fuel tank, but I dont have one, and i dont really have the money to spend on one. My only remaining option is to wire the 97's tank harness to connect with the 03 chassis harness (in a 97 OBS ;) ). I'll use the pump harness from the 03, but everything else will be from the 97 tank. I'm wondering if it will be ok without the internal pressure solenoid. I'm counting on a check engine light but I hope it doesn't effect anything. I'm not sure how well the ECU is going to cope with missing it.

Generally, emmission check engine lights don't effect performance any. Then save some money for a reflash before your next emmissions test.