Hi Roy, that does about sum it up, whatever the engine runs best with, but my Pitmans original handbook says third ring not forth for a 1959 A7SS. But count from the top as said before, I need my extra strong reading glasses to see it now when setting it up.
Mine is torch on that one however, once again this modern petrol rubbish.
Good luck with it, still waiting for my air filter to arrive from them, The carb is a far better instrument than th original.