OK, so my keys arrived from David Silver Spares today, and it turns out I'd ordered the wrong ones...
Not the Type 1, Type 2 thing - I'd got that right, but I'd ordered the keys for the early model, and it turns out they're much shorter in length than the later model keys (which is obviously the type of ignition barrel/lock set fitted to my NC30).
So, to hopefully help someone else in the future, here's what the keys look like;
Early Type 1 keys (note grooved section on left of key when holding black plastic closest to you (Type 2 keys have the grooved section on the right of the key when holding black plastic closest to you).
Critical dimensions are;
Key length overall (from tip to top of black plastic) - 60mm
Key metal part length - 34mm
Key groove length (from tip of key) - 24mm
Key max. width (near black plastic) - 9mm
Key width at narrow section - 7mm
Length of narrow section (from tip of key) - 17mm
I'll post photos of the later model keys when I receive them from DSS.