I agree, 2x 600 Edels would work nice, don't spend the cash on the 500s. I have had good luck with the 450 Holleys in the past, but it's been a long time and I have changed my tune over the last 20 years and now believe there isn't a reason to go that small
I have this discussion a lot on the internet, but remember, a small carb does not provide torque or low end like a small intake port.
A carb, only needs to have enough airflow to bring the boosters online neatly, and not too much speed in the venturi that fuel cannot be controlled at max RPM. I really like to think of the standard CFM calculation as a minimum requirement, not maximum on a common plenum intake.
It is true that intake ports and plenums can be too big and kill torque, but the carb is different, it is only trying to get airflow to pull and atomize the fuel through the main booster (and neatly travel through the other circuits). Venturi design (size and shape), booster design, float level, air cleaner, air bleeds and internal restrictions and bleeds all affect how it pulls the fuel through (actually, it gets pushed to the lower pressure side, but an engine sucking seems to make more sense for discussion)
Now, I will say if you do have a single plane intake, that is likely stealing some torque compared to a dual plane in your combo, as is the 3.00 gear, but less carb won't help that. Aside from going with a good dual plane, I'd make sure you have as quick of an advance curve as you can, and refrain from much carb spacer beyond what you need for heat control Also, if the car is a close ratio box, you'd likely LOVE a wide ratio with that setup
FWIW, I run a 1000 cfm HP series on my 4x4 F100 445 truck, and it has 3.50 gears and 32 inch tall tires. Summit has a calculator, says 632 cfm street, 800 cfm race. IMO, whoever follows those, if they are correctly calculating, now knows the expected minimum they need to fill the cylinders in that environment, and that is all. Additionally, we all know 427 Fords ran pretty good, and the same calculator at 7000 rpm says 735 street, 950 cfm race, not the 2x 600 or 2x 715 that we all have grown to love. Again, I'd call that 950 minimum, not maximum.
