^^^ This. Must have tool.
Just for grins cut off a hunk of 1/2" or so vacuum hose, stick one end in your ear, then the other end into the carb intakes one by one while idling. Guarantee you will hear each of them sucking at a different pitch. You can get them pretty close by adjusting the idle needles on each. Then observe the butterfly opening on each carb when opening the throttle linkage to the stop. Adjust the linkage so each carb butterfly opens the same amount. You can fab a feeler gauge to do this. That will get you in the ballpark. :cheers:
The vacuum hose works great on Brit and Swedish cars with side draft SU's and Webers, but I've never tried it with the Corvair Rochester carbs.