The Autolite's were never close to 500 cfm ratings. They came in sizes from around 190cfm to 465 cfm. The throttle bore size is cast into the fuel bowl on the driver's side, behind the accellerator pump rod. the smallest was .98, the largest was a 1.33. Other numbers I know of were 1.08, 1.12, 1.14, 1.21, 1.23. The 1.33 is probably the rarest and was used on the 2 bbl version of the 429.