Oh yes, I know that this post it's very old .... as I am.
At the speed of 1 or 2 MHz of clock for the CPU Z80, Arduino could became a kind of EPROM because when the CPU place the address, Arduino could put the "CODE" of this address lines and then wait for the Fetch. After this, Arduino can wait the next address, and behave as before.
It's a non sense task, but it can be interesting, because you could write a small program code in Arduino.
A strange idea.