Sorry to dig up a old thread so just to make sure I am reading this correctly a 4 barrel cast iron intake manifold will work on a 64 300? philbquick you still got that manifold and if you do its a 4bb
What was the stock carb mounted on the 4 barrel cast iron intake? I have one I am currently installing on my freshly rebuilt 1966 300 and want to put the correct stock carb back on her. The number on top of the manifold is 1366695
From the Carter AFB carb # post https://v8buick.com/index.php?threads/carter-afb-carburetors-assigned-to-buick.98044/ 1965 300 3826 A/T 1965 300 3827 S/T 1966 340 4055 A/T 1966 340 4056 S/T 1966 340 4061 California
If you don't care about numbers matching, and close would be good enough, the original AFB's were 500cfm. I would find either any Carter 500cfm AFB or get a 500cfm Edelbrock Performer with an electric choke and drive on.