the difference between the 2 engines is forged internals, and I believe the heads are slightly different. There are sti engines with closed deck blocks but there are also plenty with open deck blocks as well. You dont need the same version engine to go in the car as they are generally a straight swap as long as it is from the same phase car, however as said above dont put a wrx engine into an sti unless the ecu was swapped to a wrx ecu