It won't help much to find a casting code. Within an engine family, the different displacements are virtually identical externally and often have the same castings. Count how many valve cover bolts you have.
5=FE series
6=289/302/351W
7=429/460
8=335 series
Start here and then we can go into more detail once you figure out the engine family.

Edit: Oh and Welcome to FTE!