Another thought: Are you sure your carburetor is OK? I see that you have tried two different carbs but maybe both were a bit off?
I had a very strong fuel/exhaust smell on my Firebird earlier (much more than normal for an old car), and it didn't go very well at idle and low speeds. I thought that the idle circuit was too rich, because of the exhaust smell at idle. I then was told by a guy who is a carburetor specialist that the idle circuit was TOO LEAN. To make the engine idle at all, I had apparently turned the idle adjustment screw in so the throttle blades were opening too much, which made the carb run on the main circuit. Hence the over rich condition at idle.
It turned out that someone had tried to modify my carb and taken out a couple of small air bleed nozzles. By replacing these nozzles, I could adjust the carb back to get a strong and steady idle, and the exhaust smells are now normal for an old car.
