which 600's are they exactly? FWIW on my 360 single 4bbl engine I needed to lean the 1406 carb out about 1 step on the primary and 2 or 3 jet sizes down on the secondary.

1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)