"you can use a tachometer to achieve the highest idle rpm by adjusting each carb mixture control-- but leave the mixture adjuster alone at that point."
That would appear to be contradictory. You do have to play each carbs mixture settings against each other and that is a bit of an art. Not easy, as adjusting one carb affects the other so that using the pins doesn't necessarily give a totally positive indication of what is going on. Give the engine a rev between adjustments. If starting from a base 12 flats down note down the changes in the number of flats each time you make changes. You might be just changing by half a flat or so up and down. If you don't it's easy to lose track and you will have to start over. Max difference is usually about 1 flat, usually towards the weak side but maybe more. Check for vacuum leaks if there are big differences. Leaks around the carb spindles/carb body will mean you will never get a good consistent tune. In this case, the carbs are apparently reconditioned so this shouldn't be a problem but inlet manifold to head gasket leaks are possible.