Bit of a delay due to other commitments but the Emerald is now fitted using a piece of aluminium 150mm x 220mm (just for info for anyone who's searching in the future) picking up on the original mounts for the Rover ECU.
It fired up first time , and I have to say, checking the settings of an engine using a laptop perched in the top draw of the roll cab instead of messing about with points and mixture screws is pretty cool