The Buick castings for the 71-74 455's are the larger castings. Edelbrock used the larger castings from the early 80's Chevrolet Truck engines to make their "850" cfm RPM q-jets. They were nothing more than recalibrated standard units. Your Buick 455 carb will flow as much as, if not slightly more than the Edelbrock 850 unit.....Cliff