This spring, in the name of citizen science, I've taken to trying different methods of cleaning spare parts that I've accumulated. These experiments have revealed some odd numerical stampings on a spare block, head and cam that I never noticed before (given that they were covered in crud before.)
Admittedly I have not torn down many motors in my lifetime. But I am genuinely curious and my searches haven't revealed much.
My best guesses are that the block was marked by a machine shop who had shaved off a .003", and perhaps, in an effort not to mix up customers components, stamped the cam and tower with the same numbers so that the re-assembler had a fighting chance?...they seemed too sloppy to be cam grinds...
P79 head (unknown year), F54 block (also unknown year)