Unless by some miracle there's something in the Nissan parts bin to make everything bolt up (i.e., another vehicle uses that motor and the same trans as the Z) you are looking at custom fabrication for motor mounts, a custom bell housing for the trans, and a whole lot of screwing around with various vaccum lines and other odds and ends. Then there's the cluster and ECU, which will probably have to be aftermarket. And lots of tuning.
It would probably almost be easier to rip everything down to the shell, and install the motor you want with the trans you want, the read end you want, assuming it will all more or less fit (might need to cut into the fire wall, etc.) at all, and then build the car back up around it.
Basically, if it won't bolt right up, it's a big custom job that will cost insane amounts of money and work. Even if you do it all yourself, it's going to take a loooong time to get it together. This is one of those projects where the car will probably be on a lift or in pieces for months (if not years).
You'd be better off either boosting the Z to get the power, or trading it in for a different car altogether.
Speaking of crazy (but more do-able) projects, I want someone to install a AWD G37 trans in a Z and boost that
