Keith's advise makes the most sense, and you can save $$ by getting a rebuilt short block from Welcome Duners
They also have a good price on the complete gasket and seal kit (which you'll need). I have one of their blocks in my car, 45K miles + two seasons of track abuse so far, and have used a couple more in cars I've rebuilt and sold. They use ACL race bearings and warranty them (one year, same as Subaru)
By the time you get the old block with spun bearings apart, find the damage, get the crank and rods machined or replaced, find over-sized bearing sets etc., you'll be in a ton of time and money.
Keep in mind that you'll also need to replace the oil cooler and pump, since it sounds like both blocks have metal in them. You can clean the pump out, but the cooler is pretty much impossible to get all the shrapnel out of. Also, make sure that your turbo doesn't have little bits of metal in it, too or it'll take out the new block.
Full shop manual can be found here Impreza Manuals | ken-gilbert.com
with all the instructions you'll need, including important stuff like torque specs, valve clearance etc.