If you use any of the carb calculators on the web, you will find the 351C specs out to something less than 650 CFMs. If you plan to drive your car on the street, that is far more than enough. That said, many will tell you to put a 750 on it because you will most certainly be running it wide open all the time generating maximum HP in stop and go traffic :-). Sounds like you should install what you have and drive the car for a while. A new manifold and carb will cost you $1500 at least.
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