What I tried to tell you is a "500" isn't needed, a 350 is plenty of carb as it will flow over 700CFM @ 1 atmosphere of boost.
The carb I used was an SU, with 2" throttle plate. It makes for a very simple system using the early Buick turbo. The only difficult part was the learning curve on the fuel curve, having to make my own metering rods. I built it nearly 20 years ago and my stepson has it still.
