Quote:

so its overcarbed with a 750, contoured bowls,


stock engine, and you're looking for good manners, is not a good match for a carb with an emphasis on high speed airflow. Does it even have a choke?

Depending on the year, and whether it is a california package, an OEM carb including Holleys will have a vent that closes when the engine is off. Take a look at a CAP equiped 383 and copy that.

The Holley 4150/60 style carb has one other weakness in terms of sitting around, if the seal of the fuel bowl gasket isn't perfect, fuel will seep out that way too. For a car that sits a long time, Holley brown or blue gaskets are best, the bowl screws need to be tightened enough and evenly, and no distortion.

The biggest problem with the new fuels is the curve. It's not just the eth, but that's a big contributor. Go spill some some alcohol and you know how fast that evaporates at room temperature.

I agree with the possibility that the line from the fuel pump to the carb may loose some of its fill as well. But if the fuel bowls remain full, the engine would catch after just a crank or two (assuming there is a choke).

Quick checks. First - 4150/60 style carbs have a fuel sight plug on the side of each bowl. SO take a look to see (small pen light may be needed) if there's fuel in the bowls. It needs to almost at the level of the plug or in the middle of the window on some of the newer versions.
Take the aircleaner lid off. Work the throttle and see if fuel squirts out and into the front two barrels (holes). If not, there's no fuel in the accelerator pump, and probably none in the bowl. The acceperator pump is another place fuel can seep out on a 4150/60 model.

There's introductory explanations to carbs, afbs, oem Holleys, and emmission packages over at the imperial club dot org. Look for the Chrysler Master Technician Conference booklets from the mid 60s into the 70s.