Please help. I am trying to select right carburetor.  I really like Holley Street avenger series so 770cfm was my choice but I'm afraid that will be too much.

I have a 70 cutlass 350  Lunati voodoo cam Duration @ .050 (Int/Exh): 213/219 , Gross Valve Lift (Int/Exh): .485/.499
Comp cam magnum roller rocker arms, lunati valve springs, longer pushrods, perfomer manifold, hooker ceramic coated headers, msd ready to run billet ignition, Cloyes true double roller timing chain set.
Stock crank and pistons(refreshed)
Please help 670 or 770cfm
   

I would use a 600 cfm carb. on that combo.  

That carb is too big for a 350, nothing bigger than a 650 CFM carb for your motor, but with your mild cam, something a little bit below 650 would probably be best.  

Yea go with 650CFM because of the 350 and get holley  

I can tell you that my combo (350 Olds) has the big block heads on it, a slightly milder cam, performer RPM intake, and a bit more displacement (367 cid) from a major over-bore...and the 750 is WAY too much.  I'm honestly going to buy a Q-jet (love those small primaries) or a 650 for it and put the 750 Holley on my 425 powered Delta 88.  The 750 sounds cool when rattling off specs...but in the end performance will suffer.