Alright,

I Am planing on putting the STi long block into my WRX. I have the long block, wiring harness, and ECU from the STi, as well as the WRX wiring and ECU (and a blown WRX block). What is the EASYIST way to put this engine into this car with the least amount of rewiring/work? I know the engine is bolt up, and I didn't think it took a lot of rewiring, help?

you might not have to do any wiring, you might just have to put the engine in and connect the ECU. If no one with more knowledge posts i would try that and see if it works. The WRX engine and STi engine probobly have all of the same sensors and what not so you can jsut put the engine in and plug in the STi ECU and hopefully that should work. Dont take my work for it i dont know im jsut guessing.

is actually a lot more involved than that because an 05 STI is DBW (drive by wire) and your 03 is not so you would also need the STI pedals and use the complete harness to make it work as far as I know.

edit: nevermind. they are right. its not drive-by-wire. I always thought it was when I had mine, but I was wrong.

You also might want to think about your drivetrain too. WRX tranny and diff will be something which will require an upgrade soon if not now.

first off, a 2003 wrx is NOT drive by wire. Next, if you don't have everything this swap is going to be a pain in the ass due to the immobilizer set up. for '05's and above you should make sure you get your swaps from someone who knows all about them and will give you everything (i.e. ignition, ecu, immobilizer, im box, keys, etc.) or make sure YOU just get the whole car. The pedals are the easy part, you only need the gas pedal assembly and will need to make a bracket for it to fit. Let me know if you have any other questions, I've done a few of these swaps.
Cheers,
Joel