ylexot wasn't top discriptive but i will try to fill in. The 500 cfm of a 2V will always get me at a bad idea. The throdle bores will be way to big for most lowend torque for a small block and not enough high end for a BB. A 4V carb will be alot better because the primarys will have small bores for low end and kick in the secondarys larger bores for the highend. Go for a small 4v carb you will thank yourself in the end. on a side note for gas insted of performance you will lose so much gas for nothing with such a big cfm 2v carb.
I have no idea where some people get their ideas. The 2300 series 2V carb in terms of throttle bores, etc is exactly the same as Holley's 4V (4150 series IIRR). In terms of flow, Fords use a square bore design where GM uses a spread bore design (for the most part) meaning the primary's on the Fords are the approximate same size as the secondaries on the 4V's. Therfor, a spreadbore will give better mileage because of the smaller primaries, but.....in most cases, a spreadbore on a Ford squarebore manifold application will not perform as well as a squarebore on a squarebore manifold because of the slight port mismatch, though it really isn't that big of a deal for the daily driver, but it would drive me nuts!
2v's and 4V's use different formulas to rate CFM. To compare apples to apples, you must multiple the 2V rating by 1.4 to compare to a 4V.
Now lets chat about the 2300 series 500 cfm unit. It is an excellent unit in terms of drivability, mileage and performance. Because of it's 4V basic type design, it will provide very good throttle response at low rpm. The 500 cfm unit uses a 50cc squirter (power valve) just like the 4V.
If you feel you need more CFM (which for a stock application I doubt), the carb can be easlily modified to flow up to 550, and with a little more time and $ up to 600+. Holley makes a racing version of the carb (which is somewhat different in design) that flows 680 right out of the box and can be made toflow over 700. As a matter of fact, Pat Musi a few years ago took the championship running 4- 2V carbs!
In terms of gas mileage, depending on your "foot weight", figure around 20 mpg depending if you have an auto (a little less) or a stick (a little more).
Now with regards to your application, the 2V will work very well with that application, however compared to the performance of a well tuned 4V, I think you would be better off with the 4V unit. Reason, it's a 4v manifold with the elevated design gives or induces increased throttle response, just don't over-carb the engine (like many tend to do). A slightly undersized 4V will out perform an over-sized 4V any day of the week.....remember our engines are designed to use torque as their predominent benefactor compared to horsepower. Keeping that in mind, you should do fine.
BTW, the differenc in performance between a 2 & 4v in your application, would be powerband so to speak.... the 2V would be stronger 0-50 mph where the 4V would be stronger at 70+ mph just because of the fuel flow.
I've had personal exp. with a 500cfm 2v holley and i find the 525 demon is alot more balenced and has smaller primary bores that gave me more low-end after the switch(i have a 2-4 adapter for an edlebrock performer so the intake was the same.
One thing I keep in mind when replying to carb posts is this: Most people do not want to have to fool with the carb. They basically want to bolt and go with one or two tweakings.
That aside, I will admit I am a freak, and will d1ck with a carb until it is right. Certainly one can get good performance out of the Holley 2300. Heck, it is the mainstay of many a circle track. As far as casual roadster use, I think it is a mistake. It is far easier to over carb your not built 302 with a big @ss 2V versus a properly sized 4V carb than not. And just where do most streeter's want their performance? I'd say light to light (not that my sig says anything about it) instead of open highway run. There's a big lag if you dump the butterfly's on a fat 2V with the reg cam. I had a 1.33 (424cfm) on a stock 289 (SWMBO's), what a pig! That thing only liked it when you were already wailing down the road. The 1.14 (300cfm) is much snappier off the line. It will labor to pass someone if you are already doing 75, but what do want for a 2V?
Just my 0.02...