There are a lot of threads and some sticky's about turbo failures and what to do.
I went with a vf52 but you will need to have the car tuned for that turbo. Which by the way is a good idea for the car even in stock form. The factory timing map is not perfect.
I think a vf46 is another direct bolt on too.
If you plan to stay at oem power levels, I would still go with the vf52 and get the tuned by a tuner. The tune is the most important part in keeping the engine healthy for a long time.
Subaru won't admit to that, but there is a ton of proof on the forums.
Oh I also removed the studs from the up pipe and used bolts the dealership gave me to install the turbo, it was much easier then the studs.
You should also have the oem up pipe removed and a catless one installed. It's much safer the nthe catted one, Subaru even figured that one out in later model years.
178,000+ miles, 5/20/12 new ej257 short block, 8/20/11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
Engine Build - Click Here