"Hack your ECU"? It's just a simple tune at most...and regardless, the 255 and 257 SB's are functionally identical with small piston differences, in fact IIRC the 257 has a lower compression ratio to handle the higher boost of the STI. I don't know of any reason you couldn't run a stock tune with a 257 SB in place of a 255 SB, all else being equal.If you look here: Subaru EJ engine - Wikipedia it will show that it was used in the older Forester XT models, MY 04-05. If you plan on using it, you'll need to hack your ECU, etc.....IMHO, I would not use the EJ257 engine in your MY 10. You should be looking for the EJ255 short block.
thanks for verifying. I am picking my block up this week