I assume though even if these numbers have been removed at sometime the engine is not the original engine the pickup was built with, because the truck is a 51, the block is a 49 and the head is from 51. Are my assumptions correct?
Aye yep
My various old GM trucks have had 50/50 titles/registration using the engine ID or the body/cab plate ID, with a different ID location used in different trucks in two states.
Also, I have a 54/55 GMC with a replacement engine with a smooth boss with only the engine size on it (270); and, a 54 truck 235 with the old engine ID ground off altogether. In either case, I could punch any code I wanted into the boss. There was not need to do that in NY.
