Carb size?

that'll be fine, if you're running stock heads it won't be making much power up top anyway. The 600 will give you good throttle response and street maners.

Personally, I'd use a Holley vacuum secondary 600cfm carb, but either way, you'll be fine as long as you use a smallish carb with vacuum secondaries.

I'm not sure if you could call it much of and "advantage", but I feel they are easier to work with and every auto parts store on the planet has parts for them. That may not seem like a big deal when the carb is new, but 10 years from now, when you need a part for the carb in the middle of nowhere, you'll think it's a big advantage. There is a lot of aftermarket support for the whole line of Holley carbs, including rebuild kits and that's always a good thing. Plus, I've never had any trouble with Holleys that weren't my own fault, like not running a regulator with an electric pump, or letting the car sit for two years without draining the bowls. Other than that, the Holley carbs I've used have been trouble-free and provide great performance and fuel economy. I know other people feel the Edelbrock/Carter/Weber carb is every bit as good, but I don't know enough about them to say which is better, so why change what's worked for me in the past?

If you're not skilled at Holley tuning, a 600cfm will be fine, but I ran a 750 vacuum secondary with out of the box jets for many years on a basically stock 351 and it ran great.

Holley carbs offer the quick spring change option, where you can control when your 4 barrells kick in. thats what i like about the holleys. edelbrock is equal in performance but more complex when working on.

Complex? I changed the jets and springs in my 600 in less than 10 minutes yesterday. I do agree that Holley's are nice because of the availability of parts. I just never had much luck with 'em.