Yes, the 2.5 STI short block and the 2.0 WRX heads are a potent combination.. It's currently what I am running.. I would also suggest spending an extra 400 on Forged CP Pistons since it's easy as pie to swap them when the block is fresh.. That way you can boost up to 24psi with a 64lb turbine turbo down the road with no worries.. I also agree with Stacy about ARP head studs and Cometic gaskets, both actually on my car as well. As for porting I would suggest Axis Power Racing Stage 1 for your heads if your not planning on going Crazy.. I have their Stage 2 and I couldn't be any happier.. I have hugh valves and a wicked cam and my Vacuum is still decent and I have a strong flow through my power band.. They do VERY nice work, give RON a call..
STI short block - 1700 through a Subaru Dealer
ARP Head studs - 200 through Axis Power Racing
Cometic Head Gaskets - 150 through Axis Power Racing
CP Pistons - 600 through Axis Power Racing
Stage 1 Heads - 1200 Through Axis Power Racing.
Know I know that adds up to 4000 bug Ron is cool and will discount parts if you purchase it all through him, he did for me, and he will also put the pistons into the block, and bolt the heads on for you.. He is a good guy and builds good motors, he played a major role in mine.. If you talk to him and ask for some help he is very willing to do so.. I spent so much through him that he assembled mine all free...
02 WRX.. "It's fun when it runs.. Problem is that it hardly ever does..."