exhausts

will a Volvo V70 T5 exhaust fit a bog standard v70 2.5 10V?

Cat back, or full system from the manifold?

I am assuming that it does not include a cat. All I know is that the silencer is going.

exhaust cross reference 

you will be able to view the various components and application list here, just insert your model, etc

I would imagine the main differences would be on the length of the front pipe from cat to manifold if a full system. Then there's what bore the pipe is. Then the hole for the lambda probe after the cat will need blocking if you only have one probe before the cat.