@CBODY67 and
@Knebel : Yours and my last posts was lost, but I had read them just before. So I will reply from memory, but I am not sure who suggested what.
In any case thank you for your thoughts!
I agree the round-about incident was leading your thoughts to fuel or float issue. Unfortunately no other evidence towards this. I have an electric fuel pump and a return style regulator and have verified it flows plenty even at low fuel levels in the tank.
The ignition coil was changed to a blue streak brand, as it was the original one from 1966 in the car.
Also the carb has been opened many times and I have adjusted float level with no real change in this surging. This also means, there is no debris in the float bowls.
About the timing chain; I know it is not a potential immediate failure, but I might do it just to get peace of mind. I have ordered the summit brand double roller, which has good reviews on this forum.
I managed to buy a Holley 4160 for the equivalent of $40. It does not seem very used. If I want to try it, I have to make an adapter, since my manifold has the original narrow AFB bolt pattern (shared with the spread bore carbs) and the 4160 has the square bore pattern.
So at the moment I am wondering, if I should change the carburetor first, or the timing chain....