I would try to run it for a second with out filter just a minute to see if it improves it could be the fuel filter is do dense I think they rate then in microns or something, or go to electric fuel pump set up with aftermarket fuel pressure reg.
There should always be enough fuel in the carb bowls to start the car and get the fuel to refill them once you start pumping fuel again. this should not be an issue.As for the fuel filter being dry , if it's vertical fuel could be back siphoning right back to the tank everytime u shut it off
It's certainly worth pulling the carb apart to take a look inside. I know Holley had a lot of problems with the coatings inside the carbs for a while being compatable with the increasing amounts of ethanol in the fuel. Those problems have since been resolved for several years but there is no saying that a few carbs from that time period aren't still floating around with the same problems.I gota say also the horrible fuel these days plagued all my quads with varnishing and water accumulating in tank from ethanol a carbs a carb , I woul think a mustang sitting alot would be perfect candidate for it
Dump a little gas down the carb and see if you can get it to primeYeah sucks to have to pull the carb apart but would be worth it's weight to ease the mind