Not sure this intake will feed 600 hp

I've seen no one comment on what KIND of intake that is. It's an Offenhauser. They only made that intake for the 273 and 318 port sizes. So the answer is no way in HECK will that thing flow 600HP. A couple more things. If you look at vehicle specs that were available with two fours from the factory, generally, the extra carburetor was good for "only" somewhere around 25-35 HP. So given all that info, the estimate in post #29 is probably close, but I'd say even less.