Thanks @IG-88
I guess now I just need to work out which Slot is which in my Microserver as far as DSM is concerned and transfer everything to the genuine 1815+ that is sitting in my wardrobe that I've just never got round to moving the drives to for fear of everything crashing.
The recovery worked amazingly well - the only issue I encountered were my bonded ethernet ports - I had to move to a single port on my switch, then put the 4 cables back in their original switch port and reboot, after that everything came back up.
Once again, thanks for the information and I hope that soon we can get an EFI loader that works but I don't think it will be me who manages to do it