Truck only has same firing order if it's a 351W. Not 5.0L.The pickup motor and Mustang motor have the same firing order. It's the Windsor style firing order. If you have a mechanical pump, then the cover was swapped, or not the original engine. The Mustang went to EFI in I want to say 1987. In 1990 they didn't have the cam for a mechanical pump, and on the side the timing cover was cast in a way that the access was blocked.
First year Capri/Mustang EFI 5.0L was 1984 w/ AOD.