I've been bashing parts numbers and can't quite come to a conclusion. Some manufactures appears to tightly specify their back boxes as SH or SJ specific - others appear to lump them into one thing. Hangers visually look the same (provided the pictures I'm finding are accurate) so I'm guessing it's the location / orientation of the flanges that will make or break it.

I have a 2008 SH JDM 2.0 XT forester but I'm finding searching for SJ (FA20 turbo) yields more results.

I'm not after a complete system as the one on there's in excellent order and I just want a tone change. It'd be nice to know if someone's put SJ boxes on an SH (or tried and failed).

 

If you check NASIOC or Subaruforester.org you'll probably find more instances of changing backboxes.
They also utilise the WRXSTI back boxes (available for MY11 onwards here in the UK)