Have you tried running it without the filter? Like hook up the line out of the pump into a jar and let it pump with no filter in line? Because your pump could be bad
Rare, idk how valuable though. I mean I haven't seen a NOS one in the 2 years I've been learning about these cars. Definitely a piece for someone who really wants a perfect example of an M body
You can try flushing the pump to prime it through the fuel line from the carb using the little straw on a can of flammable brake cleaner or, if you're really good, get a little gasoline down there.
If you don't get anything the pump either lost it's prime or it's toast. Those are my guesses
This is something that belongs on a parade/show car. People complain about Aspen/Volare grilles, but the Diplomat grilles rarely pop up. I mostly see Plymouth ones.
Welcome! You could always disguse it as a 340. Get a date coded timing cover, the right valve covers, smudge the numbers on the front of the cylinder head, and add an unsilenced air cleaner, and who would ever know?