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.
The 5.0L engine in the LTD LX/Police Package (1984-85) and Marquis LTS (1985) was "H.O." Same engine that was in the 1984-85 5.0L Capri/Mustang w/ AOD.About 15HP....but that's assuming the engine was a 5.0L high output, and not something out of a LTD or other anemic 5.0 car.
165 HP in 1984
165 or 180 HP in 1985