Vapor Lock 70 Dart Swinger 340 Car
After a drive and parking car for just a few minutes I can see fuel bubbling in the clear fuel filter just before the carb
That is normal.
Car thus far has restarted only when accelerator is floored when cranking it over. Previous owner said it died during a longer drive and they could only get it to start after letting it cool down overnight.
This part is not normal. It should start hot with thottle closed and no choke or throttle just cracked open a bit.
Would love to see some photos of the engine bay.
Next time you take it for a short drive, when you get back, remove the air cleaner and look down the carb throats. Choke should still be open so you can do this without touching the throttle. Is it visibly wet? Close the hood and let it heat soak and look again. Is it wet?
If it is then the fuel level in the bowl is too high. Next will be to figure out why.
If its not, then maybe the idle is set too rich - which will be ok for a cold start but not a hot restart.
or maybe its something else but lets start here with what you suspect - which is flooding.
I have an electric fuel pump in my shop that works with existing mechanical pump.
If there was vapor lock in the suction line, then one could say that pressuring fuel from inside or near the fuel tank will make it harder for vapor to form. But your observation is bubbles in the pressure side of the fuel pump, and you suspect flooding. The flooding is either expanding fuel or pressure overcoming the needle and seat. As discussed a vapor return line could help, or a even fuel pump with the relief pinhole in it (factory around 1972). But as stated above, I think the first thing to do is physically confirm what is going on and you may be able ot address it directly.