cfm= [(displacement of engine) x (max rpm you plan to run engine at)] divided by 3456.
so (302x7000)/3456=611.7cfm or a 615 roughly.
i wouldn't do anything over 650cfm. if u need more fuel just have it jetted. i have an edelbrock an its nice. there aren't as many parts as a holley, plus your not blowing power valves from time to time. another nice thing about the edel's is they come pretty close to being already set up and just need a little tweaking with the idle mix. not that holleys arent nice though, just my preference.
I have a Carter 625 on my 351W with Edebrock RPM cam and intake, LT's, 21/2 pipes. Works great. If you drive the car alot, I'd go with the Carter or Edelbrock. They are more reliable as daily drivers. If you are building a strip monster go Holley.
Edels are good carbs for daily driving but i wouldn't touch one for even occasional racing vs. a Holley. Holleys are just as reliable and streetable, they just require a bit more user attention, but they yield better performance in return.