First the good: I swapped the carburettors and the carb mounts on Brown and it has helped with the high tickover I've been having. I had to use some silicone sealant because I've no gaskets so that might've helped. I had to tension the fanbelt because it was slipping and the associated noise was a constant reminder. I was planning on going to work tomorrow in this car so I'm all set.
Now for the bad: Becky II's clutch has been slipping for quite some time and it seems to have got worse. I'm considering taking this car out of use (she does the 45 mile commute to and from York where I work) until the clutch is replaced. I'm just waiting for the clutch kit to arrive and then I can crack on with it.