Done! Can actually use it as an armrest while driving!
Moved the hinge forward about 30mm on the armrest to move it back a bit so it wasn't interfering with the handbrake as much. Also, to hide the hinge when looking from behind.
Ended up using some bigger spacers than the ones on this pic, and used these ones to help support where the hinge sits on the centre console.
This meant that the tray under the rest stuck out...
So chopped out the same amount as I moved the hinge forward.
Then glued it together and strengthened it with some wooden bead.
Could do with finishing it to hide the joint
I'm going to add the catch and the little rubber feet off the old armrest so that it sits in place nicer, but for now I've just popped some draft excluder tape on to support the front a bit more.
Have to slide the rest back to be able to use the handbrake, but I don't think that will be a problem.