FYI, Copper is the best material for Heat Exchange...Better than Aluminum...
Use a Radiator from any year Subaru if you want, just have to cut rubber hoses to suit...Improvise and be Resourceful if you have to...I wouldn't pay $1300 for a Radiator...You can get Bar's Leak Radiator Sealant and just add that to the water...You will be surprised at how well it works...
Also, run your Radiator with only water and one bottle of Redline WaterWetter...Put coolant into your Coolant Reservoir and that will get you the best cooling results...
Water is the best coolant...Coolant only prevents rusting and lubricates your water pump...But the Redline WaterWetter will do this without taking away from the cooling properties of the water...
http://www.barsproducts.com/product.cfm?id=38
http://www.redlineoil.com/products_coolant.asp