Well, not so much a chop as a quick whip-out-and-have-a-look.
After a couple of hours of whizzing round town and a leg-stretch on the A40, I got home and pulled the plugs to see how things were cooking in the Bonnie's insides. I was expecting a black, sooty mess. Instead, I got this:
It's a poor photo (iPhone camera), and it doesn't really show the colours properly, but the results were good. Both plugs were an even pale brown, one slightly darker than the other, on the insulators and the tips. No signs of overheating, fouling or over-richness. Pretty much what I would expect from an engine running the correct mixture and in the peak of health.
I am going to be on the road for most of tomorrow, so maybe I will get the chance to do a roadside plug chop to see what it's like at 3/4 and full throttle, but it looks as though those 140 main jets were in the right zone, at least.