It's taken a lot longer than I thought, but it's is now ready to test.

There has been some issues to address in the assembly:

Power supply - the power supply I had for this simply didn't fit one the buttons were in place. A 5V 3A phone charger was shelled and used instead.

Pi orientation - the aim was to have the usb ports poking out the back of the case, with the board munted upside down, but the dimensions of the hat made this undoable. The usb ports aren't needed, so it's not a huge loss.

Lastly I'd imagine some shielding will be needed to reduce interference, so on the lookout for some pretty shielding suggestions ha ha!