Oscilloscope arrived 
The Nano is producing a good 1Mhz pulse of 5V. I am now using USB as the only power source and have joined GND and +5V of the two boards.
Does this look OK? There are some spikes but that's OK right?)
Unfortunately I still get nothing.
My next check will be to add a third Nano (thank god they're cheap from eBay) to begin from scratch and try and read the 8 output bits and directly print to the serial monitor.
I noticed the Nano pins like to jump out of the breadboard and mess up the signal, but now I am aware of that and I'm still getting no readings.