Does anyone know if that's actually a Murano rear sub? I can't find any pictures of one, but it could be out of an FX and the junkyard is dumb. The only difference I know of is that diff mount bolt is a different size.

This is supposedly a Murano from 2004 or 5, and looks different:



Here's a photo of the FX back when my diff was clean.

 

CF driveshaft in a production car for a resonable price is one thing that really impressed me about Nissan. I used to be a domestic only enthusiast.
As far as OP is asking, I would not bother switching in the murano rear. I am sure the engineering will not hold the torqe of the vq. If you want to upgrade the rear of the z, there are plenty of parts that are specific to what you want to do. I will never knock someone pioneering there own build, but to me this one doesn't make sense.

Either way I wish you luck on your endevours.

 

It's possible the rear subframe is from an Infiniti FX, as it's also built on the FM (front-midship) chassis. But who knows? As I stated in post #15, junkyards may use erroneous descriptions for many cars. The only thing for sure is that's not a rear end out of a Murano...

 

So FX's should have a 19mm nut that mounts to the diff as shown in those pics. Z should have 17mm. From my understanding the bolt is smaller on the Z, which is why I can't swap to a solid or poly bushing on the FX without some modification somewhere.

OP, you could check that nut size and it might help answer your question somewhat.