"...If you are over carbed with a Holley 670 you will be over carbed with a 750 or 800 CFM Rochester..."
Well, I'm sorry, but I'll just have to disagree with that statement. Both 750 and 800cfm Q-jets came on LOTS of 350's. Hey, some of the 301's even came with the 800's.
That's one of the great things about the Q-jet. If properly tuned, it will provide everything from good street manners for a DD 301 engine to plenty of fuel for a 450hp street 455, or 9 sec ET's for Super Stock drag engines. Even some of the OHC six engines had Q-jets.