That makes sense... I didn't see how an Impreza rad would be big enough. Do you know if the Outback one was from a 4 or 6 cylinder? I would have thought that maybe one from a 6 would have the capacity... but maybe not!
I did come across this post on Facebook. I sent an email to the shop asking if they recall what parts they used and the overall complexity of the installation.
It seems like there are some alternatives out there, but they just might not be documented very well anywhere.