Not much; Zorro is basically the 68000 bus protocol, while NuBus is more general. But it's just a multiplexed address/data bus with a selectable 8/16/32-bit l word size for data transfers, it can be implemented with a simple state machine.

All you really need are the level shifting buffers just as with the Zorro interface, and enough I/O for the 50-some NuBus signals. That breaks down to 32 address/data lines, a few NuBus control lines, and some lines to control the level shifting buffers.