Much depends on other engine mods (specifically camshaft). I ran a Carter 400 on a stock 300 CID Ford and it was plenty.

This article may help:

http://www.thecarburetorshop.com/Carburetorsizeselection.htm

Or possibly this one:

http://www.thecarburetorshop.com/Carbshop_carbsizesandCFM.htm

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop