The NV5600 has a separate bellhousing whereas the ZF has an integral case - so you would need a GM ZF for it to have the standard GM V8 bellhousing bolt pattern. The GM ZFs were pretty scarce, so you may have difficulty finding one and pay a premium for it.
Other differences are that the NVs are cast iron while the ZF is aluminum. So the ZF is lighter, but also quite a bit bigger in size - figure in some sheetmetal work to the floorplan or a lift to get it to fit.