Here are the different radiators I've found for the SVX so far:
OEM Subaru "Radiator Assembly" P/N 45199PA001 MSRP: $425, SubaruParts.com: $378, SubaruGenuineParts.com: $363
Silla, P/N 7420, $165 (several places online)
Plastic tank (like OEM), lifetime limited warranty
Replacement (brand), P/N P2083, $200 (several places online)
All metal? (one place said so, but others show "plastic core") 1 year warranty
Spectra Premium Radiator, P/N CU2083, AdvanceAutoParts.com $335
(also PartsAmerica.com, who is also affiliated with Advance, Checker, Schuck's, and Kragen auto parts stores)
P/N is suspiciously same as "Replacement" brand
2 Year Limited Warranty
PWR, P/N PWR5229,
PWR-Performance.com $599
(group buy on here awhile back was $450)
I'm seeing $540 on a current eBay listing
All-aluminum
A large and reputable radiator shop here (in business since 1949) says they have had poor results trying to replace the plastic tank with a new one — the mounting tabs don't hold up. They said they also won't solder on a replacement metal tank — when they've tried in the past, it caused problems with the welds on the core tubes/fins. Ordinarily they will do radiator repair and refurbishments, so I doubt the reason is that they just don't want to bother.