383 ci 7500 RPM with 100% VE = 831 CFM
383 ci 7500 RPM with 92% VE = 764 CFM
That's what the figures say, but they do sound low to me.
I ran a 351C to 6000-6500 RPM and according to this the 600 CFM (1850 Holley) that I started out with should have done the job. Not so ... it seemed to run out of breath around 5500. I upgraded to a 750 CFM (3310 ) and that seemed to do the trick.
I'd suggest asking a buddy to borrow something a little bigger (850 CFM) and give that a trial pass.