Thoughts on Carter Carbs

Im looking at an offenhauser 2x4 intake that is a single plane with Carter AFB 500 CFM carbs. The carb numbers are H7 9500 A. The front carb has a choke and the rear one does not. My question would be how well do they work on a performance car, how tunable are they for performance and how available are parts to play with. Its been so long since i've had one of these apart (25 years or more) and when I used to rebuild them at work it was for the stock engines only. Do you know if this model number has jets that can be changed or just the metering rods. Do they have upgrades for accelerator pumps? The linkage would be a progressive style. I would guess upgraded parts would be more expensive then holleys because of the availablility?
I would be using on my 408 instead of the Edelbrock tunnel ram and holleys I currently have.
I appreciate any help and information you can throw my way.
Thanks Rod