I have mustangs also, I ve replaced fuel pumps before and even new pumps can be bad. Sitting on the shelf for so long and being bumped around in shipping. Check the fuel pump, then work your way to the filter then work your way to the carb. Carb jets can also be clogged.
If your 1965 Mustang 289 is still not getting gas to carburetor after replacing the fuel filter, then you should check the fuel line. You should remove the fuel line from the carburetor and inspect it for any faults.