If your intake is a spread bore then you should use a spread bore carb.
I like the edelbrock RPM intake (not rpm air gap) with a holley 3310 (750 vacuum secondary) on just about any street/strip chevy V8 build. Works well on street driven engines up to 450hp.
Get a 750 cfm if you get a vacuum secondary carb. Or a 650 cfm with mechanical secondarys.