[JerryL]

Briefly with your description(s) So adjusting vacuum sounds like you have all 6pulling identical vacuum, GREAT!!
You also say screws not touching the arm / stop, Hmm?
Main linkage cross bar with the 2 arms (1 to each carb) unsnap the short arms going to each carb lever arm, this should release the linkage to seat on the idle adjustment screw on each carb set, (10 : 1 your idle will drop off).
With the 2 arms disconncted from the carbs get the idle RPM right balancing btw the 2 carb sets, you will see one or the other adjustment screw touching, slowly get them both at about the same position a bit at a time keeping both drawing same air till you get the idle you like.
Then adjust the length of the 2 lever arms from main lnkage to each carb to where you can snap them on without changing the idle rpm and you are done.

You may well want to lube the linkage and the carb shaft areas as well to prevent any binding.

Regards