On my 1975 Series 4, with 400ci engine, I initially replaced the original Carter with an Edelbrock Performer 750cfm, with electronic choke. It worked well out of the box and better with some rolling road adjustment. The car is mostly for long distance touring, not pedal to the metal, but plenty of fast motorway type cruising and I would say very satisfactory. On a long run returning 17-18mpg, with good acceleration and torque through the range. The car is also fitted with longer 603 rear axle.
I then switched to the Edelbrock 1902 AVS2 650cfm with electronic choke, because I read that it has a more sophisticated jetting system, and also was persuaded by comments that perhaps 750cfm is over-carbed for this engine. In practice the difference in driving is not noticeable at all. Similar torque and acceleration through the range. The 650cfm actually returned slightly lower mpg at 15-16 over a long run. I did not test either at the extremes of torque or revs (are any V8 Bristols are driven on the limit?), but pretty happy with both overall. I will probably switch back to the 750cfm unit for next long trip.
It might not be the same for your 383, which I think has slightly higher compression, but suspect it will not be a lot different. Also I doubt there is a lot of difference between equivalent Holley and Edelbrock units). From some other threads, it seems that to make bigger steps in performance/efficiency you should consider efi options, but this needs more complex setup and installation.
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