So after much messing around I've found the issue wasn't the SD cards or how I formatted them etc.
The issue is a dodgy connection between the NGCD mainboard and the SD Loader, and I can't seem to get a connection that is stable and reliable. The SD loader board doesn't 'click' into place like the installation instructions suggests, so maybe the socket is defective. If I push the two together hard there is a connection but over a period of time the connection breaks, especially if I move the system (for example putting it all back together results in a lost connection). Very frustrating. Furrtek still hasn't responded to my initial email and didn't respond to my tweet, so I'll send a follow-up email now that I actually know what the problem is to see if there's anything that can be done.
Once the NGCD that I'm waiting for arrives, I'll be able to progress the install and it'll be interesting to see how one of the other SD Loader kits fits. Hopefully I'll get that reassuring click when putting the two together and I'll be happy to return it to the customer with confidence that it'll be secure. Right now, with the system I've done so far (mine), I can guarantee it wouldn't work if I had to move it off this desk, let alone if it was posted anywhere.
UPDATE: Now the left direction isn't working on the pad. Ever get the feeling you never should have started something?
*goes off to fault-find the controller board...*