Just updating this project, as it has been a while!
I have all the parts required to make exactly what I need.
I've drilled a few holes where required to allow for cables to be passed from the head unit, to the display area, and also to tap power to the Mauseberry circuit.
Before proceeding, however, I have a few wiring issues to fathom.
I've recently replaced the stalks on the steering wheel as my headlights would come on while indicating right, and that issue has been sorted.
Another is the brake lights seemingly sticking on, so hoping the switch behind the brake pedal just needs replacing.
Intermittent cabin lights are also an issue.
My favourite quirk has to be that when wipers are on and the driver window is being closed turning the steering wheel right can put the window back down, ha ha ha!
I'm hoping to find whatever short is causing these soon; once I have faith in my wiring I'll be able to add the head unit.