Well, the diesel's all gone, and the misfire turned out to be a leaky manifold gasket (causing a fault on only one cylinder, not 2, which is why I thought it was something else).
But every so often the engine just cuts out, although liberal amounts of choke pick it back up if I'm quick enough. Most often seems to do this either when flooring it, or when trickling along at part throttle, in traffic. It's also running far too rich, or at least smells that way, but any leaner and it runs rough. My first thought is the carb is worn, maybe a combination of faults including where the spindle goes through, and possibly float. But before I play with it (I think I've got a spare somewhere), I've also noticed the rev counter often twitches when the car seems to be ticking over OK - I have my suspicions this is ignition circuit related.
As it's got the electronic "points" dizzy, I'm not sure I want to start trying to diagnose any ignition fault unless I can be fairly sure there is one to start with! Does it sound like a flaky coil or ignition module could be a part of the problem?