Dude, don't do it! Even if you are turning 6200 rpm, you only need 465 cfm of carb. It is far better to have a carb that will flow your maximum need and no more than it is to have a carb that flows too much. An over sized carb will, in effect, have a whole bunch of unusable throttle underfoot and will only give "response" for the first 1/3 of the available throttle movement. After that, it will make no difference whether the throttle is at 40% or 50% all the way up to 100% of throttle. What this means is that the first 1/3 of the throttle is all that your motor can use and seeing as how the best efficiency of the carb is in the 1/3 to 2/3 range of throttle blade opening, you will never even be in the range of the boosters best efficiency flow rate at any time what so ever. Not a good start. Way better is to have a 450 cfm two barrel that your motor will be flowing at a blade opening of 1/3 to 2/3 and more where the carbs efficency and it snappy response will be available. Also, keep in mind that the "flow rate" of carbs is rated at two different vacuum settings. One is used for two barrels and another is used for the four barrels. Since four barrels are always usually bigger. it is much harder for a motor to flow enough cfm to bring a vacuum reading of 3 inches, so, they use a vacuum reading of only 1.5 inches instead of the 3.0 that is used for the two barrels. This means that a 600 four barrel, if run at a vacuum reading of 3.0 inches would have a rating that would be much higher than the 600 that they are claiming. Also keep in mind that the 465 cfm that you need is only needed when you are at 6300 rpm and your motor is going to rev still higher. Not a common environment, even at the drags, so don't sweat the fact that the cfms of the 450 doesn't meet the max flow rate of your equations. I have run as small as a 390 cfm four barrel and lost no top end, but boy was that throttle snappy? I run a 465 four barrel and it will run my 302 up to 85 miles an hour, with a 350 gear ratio in the back, on just the front two barrels. After that, I am running on all four barrels. I have 63 jets in front and 64 jets in back with a 10.5 power valve in front and a 8.5 power valve in back BUT, I also have metering blocks that have some awfully big P.V. channel restrictors that allow a whole lot of fuel to be run thru them. Few people know that up to fully 70% of the fuel comes not thru the main fuel jets, but thru the P.V. channels and in this way I can run on all four barrels at nearly WOT and still not flow all that much fuel because the P.V.'s have not opened yet. It isn't until I squeeze open the last 10% of my throttle blade opening that the vacuum drops enough to open the power valves and start to flow the 2.4 times as much fuel into the motor as I was flowing at the 90% throttle opening, one that allows me to cruise at about 126, with the WOT carrying me to a calculated 142 miles per hour, depending on the tire size and whether or not I care that it is drinking enough fuel to actually see the gas gauge dropping as I go. A two barrel for you will give this type of performance. If you now can run only 80% of your top speed with 90% of the throttle, your in good shape. If your P.V. is opening below 70% of throttle opening, you need a lower rated P.V. to keep it from opening before you get to 90% of throttle opening. If the carb gets too lean with the lower rated P.V., then increase main jet size by two numbers. Never more than five, ever. In the end, your car will need to have it's throttle opening opened and closed a great deal more than it does now. But, like a dirt bike, there is really no in-between in the throttle opening game. If you want acceleration, WOT is the way. But for the ability to cruise at high speeds and do so with as much efficiency as possible you need to have a carb that will give efficiency over a wide range of flow numbers (rpm) and one that will only flow big fuel numbers when it is needed. I heard that somewhere in America the speed limit is now 85, and that's OK with me...so long as they move over to the right and let me pass. lol
Well that was an eyefull. I will be careful to calculate exactly what I need. I will be changing the heads also so I know that will come into play. I made the mistake about 20 years ago with my S.B.C in picking a single plane high rise intake and did not have the heads to flow. It was slow as heck out of the gate but had 140 mph top end. Believe me I will not make the same mistake again.
600 on a dual plane will work just fine. Is it more carb than you need? By a small bit. Will it effect performance in a negative way? Not noticeably and it will improve over a 2bbl any day of the week. that 600 is pretty tunable but out of the box it will do you pretty well.
Wow! That was a lot less than 802 words! No I didn't count the prior oration but there is a web site that will do it for you! LOL