The Carter AFB actually has mechanical secondaries with and air valve under the clusters. The air valve keeps the huge slug of air from leaning the mixture out too much. It's still not as nice a transition as the Holley vacuum actuation system. You probably don't really need the pressure regulator, your in-tank pumps are 6 psi if I remember correctly, they are centrifugal pumps, not gear pumps like EFI and are designed for a carburetor. If someone put EFI pumps in that would explain a lot of the flooding issues with the Holley.

I have used both types or carburetors and the best match I found for a 460 was the '69 428CJ 735cfm Holley. It is a 780cfm main body with special primary booster venturiis to step the primary air flow down to 345cfm.