Saxman, I was reading in your post on the Allison thread that you were planning to overhaul your cylinder head. While you're at it you might as well have them check it for for cracks. They tend to show up in between #2 and #3 cylinder, IIRC as well as the exhaust valve seats. You mentioned earlier in this thread you had adjusted the carbs a few times, which is sounding a bit much. A leaky head gasket can affect your idle, but another might-as-well-while it's-apart you might check, is the throttle shafts on the inboard side of the SU's. Along the plane of force of the throttle linkage the shaft can wear out of round in the carb body as well as shoulder the shaft. Moss offers new shafts and bushes(IIRC) in their master rebuild carb kit.After 40+ years of service it's no surprise. I redid one for a friend about 15 years ago and he said it had never run that steady since he owned the vehicle.
One other suggestion for driveability and peace of mind would be to consider a drop-in electronic ignition when funds allow. In the mean time carry a spare points and condenser in your road kit, just in case. I recall hearing the modern condensers don't last as well as the old ones, so you might keep a few around.They're fun little cars to tinker with and keep tweeking with little improvements that make them funner and funner as you go!
As Cecil Kimber said, Safety Fast!
Got a photo of the engine room?