Well, at least I fathomed one thing out correctly and got the starter and ignition switch wired up to the right terminals. I got the engine to crank tonight - so I did put the engine and starter motor back together correctly.
Not quite as momentous as starting her up, but at least I could check the compression on the cylinders. Which seem to be spot on. Huzzah!
I think my cut off switch may turn out to be more of curse than a blessing. I've wired it up as per the instructions, and get nothing from the bottom terminals. The main chunky terminals are fine - it's just the lower spades that don't seem to be doing anything. I ended up bypassing it to check the cranking.