Do a hybrid build like I did with my '03 EJ20. If your heads are in good shape just send them off (I used and highly recommend EQ tuning and their 2.5l head mod) to get a rebuild done on them and mate them to the EJ 255 shortblock. Re-use your stock intake, turbo, etc. As long as it's all in good shape. I did this and love my new motor. You'll need to reflash the stock ecu with Cobb AP with a custom tune to run the motor as well.