EJ 205 Swap into a 2.5 rs?

Ok so i am told an EJ 205 engine is an 02-05 wrx engine, so if i swapped this into a 99-2001 2.5 rs what else would i need to do? people tell me with an sti swap i need to redo the and a bunch of other things but with the wrx could i just bically set it in there? haha how much hp would i get out of the EJ205?