Originally Posted by tlfowle
The part numbers I'm finding are 10103AC030 for 04-06 Legacy, 10103AC040 for 07-09 Legacy, 10103AC050 for 08-13 STi.
Here is a quick search to show you that the EJ255 and EJ257 are the exact same short block. For your application, a 2005 Legacy GT, you want to use part number 10103AC030. Use the link and scroll through, and you will see that part number comes up for an '05-'06 LGT (Spec. B too), '05-'07 STi, '05-'06 Baja Turbo, '06 Forester XT, and '06 Outback XT. All of these share the same short block, there is no difference. The heads and intake manifold may differ between the models, as well as what turbo comes stock with each vehicle, but the short block is the same.
Order a 10103AC030, whether it's an EJ255 or EJ257 doesn't matter, and have your heads re-finished and put them on the new block. I would order from one of the vendors here in the LGT community...best service, best prices, and you support one of our guys