Look at the fuel pump, does it have a round steel cannisiter that threads off/on?

If so, inside the cannister is: C4AZ-9365-B .. Corrogated Paper Cartridge Fuel Filter (Motorcraft FG-1A) / 1964/76 myriad FoMoCo vehicles.

This is the original location for the fuel filter on F100/350's and since some/most (pick one) people are unaware, they install an inline filter.

Meanwhile, this filter probably hasn't been changed since Reagan was prez, and so is getting more clogged up every day.