The NM35 HAS a single turbo set up.
It's low down on the passengers side, and brings a balance pipe around the top of the bellhousing, joining into the passenger side manifold. The space is limited, and this compromises manifold design, and turbo size.
I would imagine the issue with twin turbos is interference from the steering column on the drivers side. Still, there are TT kits for 350Z, and the basic architecture in the engine bay is similar, so I'd be looking that way to begin with.