With all that you have done, it does not sound like a fuel delivery problem, but still could be. I assume you have checked your timing. Have heard where the timing has moved and that's all the problem it was.
First check is of course the fuel cap/fuel tank. Your car should have come from the factory with the fuel tank with a vent tube that is visible in the trunk. The cap should be the un-vented cap when using the vented tank. Has the tank ever been changed out? Could be the wrong tank, ie a non-vented tank with the original non-vented gas cap which is causing a vacuum and not allowing gas to flow. Just for fun, when it happens again, pull over, loosen the gas cap or take it off so you don't lose it and drive it to see if the problem stops. Don't do this will a near full tank of gas and don't accelerate hard as the gas will dump, just drive it easy to see if anything changes. Could be that simple.
Do you have a fuel pressure gauge mounted that might let you know that the fuel pressure is dropping or going away when this problem happens? Might be a good investment to use in diagnosing a fuel delivery problem. You can remove it later if you don't want to keep it.
Do you have a return line going back to the tank? You could have fuel percolation problem which can be a real problem with the alcohol in the fuel and when the car is hot. Adding one could be helpful. Factory AC cars had these installed. I see RobbMc offers this as PN 1010 Vapor Return Option on the 550HP pump.
A phenolic spacer under the carb could also help as it acts as a heat insulator if the carb is getting too hot and the fuel is boiling inside.
Does your distributor have a 12volt power wire? The factory used a resistor wire for the original points type ignition. Using the factory wiring will not deliver the 12volts your electronic distributor needs and it will operate poorly and exhibit problems as you describe. You might want to make up a length of wire with alligator clips on the end of them that will reach from the Positive + side of the battery to the Positive + side of the coil. When it starts acting up, pull over and attach your test wire. CAUTION: the car will not turn off using the key with this wire attached, so you have to pull it off in order for the engine to stop. If the car runs better and problems go away when you do this, it is a power supply to the coil. Could even be a bad ignition key switch, broken wire, bad ground, or something shorting out if a wire has rubbed through. I always suggest a battery disconnect switch at the battery if you have an electrical short and wires begin melting/smoking and a good fire exstinguisher that is handy just in case with these older cars.
Have you checked the condition of the battery/alternator/voltage regulator? Low voltage can cause all kinds of problems. Make sure your battery is good and the alt. is putting out the needed volts. Local auto parts stores can usually check this if you can't. Also, if you added things to the car like big amp stereo's, electric fans, or other power drawing opetions, the factory rated amperage of the alternator may not be enough. A local guy was having this problem. Charging system checked out fine as did his battery. But his battery would go dead after crusin' for the night with lights on and the big stereo system. AMP ratings were too low for all the accessories he had going on with all his lights running at night.
Check all wires to the distib. & coil. Is the coil matched to the distrib.? Often, a hotter type coil is needed to work with the electronic ignition. These are usually recommended by the distrib. maker. Run the car in the dark at night and look for any electrical arcing or grounding.
Have you checked the advance curve of the distributor? This is very important. Could be that something is not operating as it should or is binding/sticking. Do you have a vacuum advance on the distributor?
Just a few suggestions to get you going and in a direction of narrowing down the problem. Right now it could be several things from carb, fuel, ignition, wiring, valve adjustment, etc.. So hard to figure out at this point without more input.