[HO455]

Have you checked the timing while reving the motor. Maybe your mechanical advance has gone wrong. I don't remember if you tried a different distributor cap or coil.
In the carb your primary butterflies may be open too far at idle and the off idle transfer circuit is not able to work. When you open them there is no fuel shot to keep the engine running until the accelerator pump shot arrives. So the engine stumbles then receives a big glob of fuel and basically chokes on it. If you pull the carb you can check this on the bottom of the carb. The butterflies should be in somewhere in the bottom 2/3 of the transfer slot. Definitely not above it.

I just reread the thread and most of the above is not valid as you already have swapped those components. A leak down test may reveal the problem. Leaky valve or bad head gasket are possibilities.