Rebuilt 273 won't idle

The original AFB carb in 65 has a large screw in front between the two smaller idle mixture screws found on most AFB's. It's my understanding that this screw controls air flowing through an idle circuit that bypasses the throttle plates. I believe this screw is used to set the idle speed, not a screw on the linkage, which I believe wasn't even present in 65. The linkage will have a fast idle screw for when the choke is on, but not the standard idle screw found on most carbs.

You stated that you can't get the engine to slow down. Try turning this large center screw in until the engine will idle with the throttle plates completely closed.

Then adjust the idle mixture with a vacuum gauge the way you would any other carb. Adjust the mixture screws for max vacuum and then reduce the idle speed using the large center screw and repeat until you get it idling nice at the proper RPM.