I want to put an EJ25 into my MY'00 LS wagon. Currently it has a phase II EJ18 which is on the MAP-based ECU. This setup has MAP sensor and IAT sensor in one unit, on the intake plenum. I have only one O2 sensor, before the (single) cat. This car has no EGR, no air-assist injection, no fuel tank temp/pressure sensor or solenoid valve. It does have a knock sensor however.
I can think of a few ways of doing this:

Option #1: Wire in an EJ25 ECU of similar vintage with its two cat exhaust, extra O2 sensor. Try to trick the ECU into believing the fuel tank sensors etc. exist with resistors/diodes to drop the voltages into the sensor output ranges, and some dummy loads to replace the solenoid valves.

Option #2: Use the EJ18 intake manifold, ignitor / coil pack, injectors, fuel rails, throttle body, sensors etc., basically everything, just the EJ25 long block. Keep my ECU and install an emanage with both the ignition and fuel harnesses to adjust the fueling.

Option #3: As above, but use a 99 RS25 intake manifold and injectors which I think has none of the air-assist junk on it. Use the emanage to scale the injectors to suit.

What would you choose? (please hold the suggestions for a WRX swap) I can get a brand new SOHC EJ25 long block for a very reasonable price. Probably '04 stock.

 

All right, let's put it another way. If you had an 01 RS, bored/stroked the block to 2.8l, fully ported the heads, bored the throttle body, fitted the race cams and basically did everything you possibly could to increase the air it would pump without going FI or increasing the rev limit....

What would you have to do to run it with stock injectors?