750 CFM for my 383 or what?

The 383 will devour the 600 CFM might even lean out on you at WOT. Its venitures are smaller. The 600 will get you to the grocery store. lol! Definitely go with 750. I ran a 750 Holley on a well built 383 for a long time the engine loved that carb. I was thinking about going 800 cfm but never did. Of course I use Holleys so the AVS type carbs I didn't even waste my time with. Vacuum secondaries for auto trans and mechanical secondaries for manual transmissions.