So, I have a 1991 JDM EJ20 engine that I'd like to drop in my 1998 Legacy. If I want to have any hope of registering the car in an emissions area, I need to have it capable of OBD2 goodness.

It doesn't appear that the engine changed all that much through the years, so is this possible? Can I, for instance, get a WRX(02+) ECU and mate it to the 91 EJ20 no problems?

Obviously, wiring connector is going to be different, but I can rewire the dang thing, without too much fuss.