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[font color=red size=3]I agree, I wouldn't go over 600. I have a stock 390 with an Edelbrock 600cfm, and it does great. I would also suggest that you get an Edelbrock, they are easier to tune and are more 'street friendly' than a Holley. (in my opinion - of course)
I put an Edelbrock 600cfm on an Edelbrock 4v Performer 289 manifold, on my old 302. It was fine, but the motor got pulled. I put that same carb on my 390 where it's going to stay. Now I have another 302. For now I'm leaving the 2V on it because it is working well. If I pull that motor and clean it up, I may put the Edelbrock manifold on it, but I'm going to go w/ a smaller carb like a 500cfm next for the smallblock. BTW if you are shopping for Edelbrock type carbs, the Carter AFB is the same thing and they have a 625cfm size. I found a more dramatic improvement in my smallblock by haveing the distributor rebuilt/recurved than by putting 4V on it.
According to the Holley book, your motor won't pull more then about 450 cfm so a 600cfm 4bbl is plenty big and a 500cfm 2bbl is to big (it will bog). Unless you plan on a HiPo rebuild, a Holley 390 cfm 4bbl would work great, good gas mileage and decent performance.
Been there. Done/tried that.