Well, Graham, I think you're right that I'm right!
After a hopefully-this-will-get-rid-of-the-headache morning nap (it'd be so nice if our children (7 months + 4 years) would sleep past 8am

), I went out and had a play... I stuck my head further into the boot than I ever had before, to make sure it was negative earth. When I saw the "+" was definitely going to the loom, not the chassis, I felt a little more confident.

I removed a coil mount bolt so that I could loosen the coil ring, so I could rotate it, so I could get an 8mm spanner on it (sometimes things are complicated - whoever installed it could've just left it so you could get a spanner at both terminals!

), I switched the double connection over, connected the two non-dizzy wires to the positive (instead of the negative), and hooked up the two dizzy wires. Got in the car, cranked it, smelled smoke.
Then it dawned on me I'd swapped the dizzy wires over as well as the other two.

Made up a couple of new adapter wires (double female blade for the black/negative wire, double male blade + 1 female blade for the red/positive wire - so I could splice in the three wires to the positive onto the one double male blade adapter - didn't think to go and buy a ring end to hook over the terminal, not that it would've made life much simpler), switched the wires over...
Cranked it.

Nothing.

No spark.

But no smoke, either - first time ever!

Given there's still part of the electronic ignition module that's still blue (even if the baseplate is a smoky grey), I figure that means it's now right. There's part which is still blue, meaning it's not burned as much as it could do, but it's still largely black and there's no spark, so I've killed it.
Or, is it that I've killed the coil..?
So, time to head to eBay and send another $52 to the MG guy...

Not his fault, but that doesn't make a bloke any happier.

Thanks for the offer Mick, but I'd rather burn my only own money and time than burn someone else's time as well.

Not that I'm expecting to burn the next one!
It appears I was doomed from the start, given my car is negative earth (which I checked before I bought the kit), but the coil was still wired positive earth.

And the instructions don't have a diagram with them. And, before yesterday, I was a total and complete noob at this!

I have a
little bit more of an idea now... Still a noob, but not as bad as I was 24 hours ago!