Carb CFM.. Increase?

YR is telling you venturi size for not just flow but the throttle response with it. The old way, as you say, via cfm rating, was right for the intended drag car purpose that also fit (reasonably well) hot street cars with the older Holley design carb.

If you grab an old school Holley, I’d say no less than 750 for the engine. If you grabbed a modern body worked over carb, you can do more with less, or should. The trouble is prying money out of peoples pocket for the best of anything they deem over the top for the build or what they think they can do themselves.

If you want to drop 1,000 or 1,200 or whatever for a single 4bbl. carb, be my guest. That’s your call.