Timmer - 52pu's comments concerning the W-1's is very good advice. You would want to use either the 483s or the 574s. These may be mixed or matched as the difference is basically the way Carter made the castings, not in the calibrations.
A couple of other comments: 52pu probably meant to say that the airflow through each carburetor will be half, not the vacuum. Vacuum will be reduced in each carb, but not half. The reduced airflow will cause a lower velocity in each carb, which will reduce the point of bleedover. This is an excellent reason for using the Carter W-1 carbs, as these carbs have a physical override on the power circuit; instead of the vacuum only system in the Rochesters.
And while slotting the throttle bodies is certainly an easy approach, and inexpensive; I prefer to take the intake to a good welder, have the existing holes heli-arced, and then redrill and retap. It costs more, but makes a much nicer appearing installation (MOO).
Jon.
