And here we have the battery installed (ish*) and the positive cable run from the start solenoid to the relocated battery.
*The battery cover needs some rivnuts inserted in the firewall to attach it properly.

I did have a bit of a change of mind over something...
The GDU is separate from the dash and has been wired into the firewall. But the AFR meter uses all inputs (RPM, +12V and Earth) from the dash so it makes sense to wire it into there!! I was previously planning on wiring it into a bracket on the dash! Duh!