A double pumper IS too much for a mild SBC. You need some serious mods to be able to burn all that fuel all at once.
A 350 cubic inch engine at 6500 RPM and 80% volumetric efficiency can only use 526 CFM. Anything bigger than that and you’ve overcarbed it, plain and simple, end of story. Everybody thinks that they need more carb than they really do. Yes, the engine still runs fine with a huge carb, but you do lose some low end torque and throttle response because the venturis are too big and you have a low velocity resulting in a poor mixture. Fuel economy also suffers. A 500 CFM carb would be more than fine for a street driven car. It’s 26 CFM undersize, but you’ll have better throttle response and better low RPM behavior for cruising. A 600 CFM is 74 CFM oversize so low end will suffer a bit, but the carb outflows the engine so it can reach it’s full potential. No matter what you get, you’ll still have to tune and retune it to your specific application.