* Ford 351 Windsor: The firing order is 1-5-4-2-6-3-7-8.
* Ford 351 Cleveland: The firing order is 1-3-7-2-6-5-4-8.
Therefore, you need to specify which type of 351 engine you have to get the correct firing order diagram. A diagram would simply show the cylinders numbered 1-8 on an engine schematic with the firing order sequence indicated by arrows or numbers. Many online resources (including various automotive forums and repair manuals) provide these diagrams if you search for "Ford 351 Windsor firing order diagram" or "Ford 351 Cleveland firing order diagram."