fuel issue
I’d recommend bottle feeding using a rubber line and a used antifreeze-sized bottle mounted safely near the alternator/fan housing. If it is able to mechanically pump fuel from a temporary bottle…. then, you can almost rule out the fuel pump issue. If you haven’t already, I highly recommend installing a clear Wix fuel filter just before the carburetor. This will insure that you can physically see fuel being pumped and the filter material will breath with each pump. I don’t recommend using the clear plastic filters for longer term use but, make trouble shooting gas delivery issues a lot easier to manage.
I say “most likely” rule out the fuel pump because I’ve encountered a handful of 440 motors where the metal fuel push rod was smashed shorter than OEM length. So much so that a bottle feeding would work but, pump arm movement was minimized from the shortened rod that it wasn’t forceful enough to build pressure from the full length of line to the gas tank. <— This is a very rare occurrence but, also might be worth checking the fuel rod length is oem.
New Carter fuel pumps are really hit or miss. It’s not quite 50% are good and 50% bad but, it almost feels that high of a failure rate on the newer, cheaper made, ones.