Your engine is definitely a '54 full-pressure. The number you gave is the engine serial number. For the F54ZC part of the number:
F=built at Flint plant
54=model year
ZC=engine ID suffix as translated above.
The block casting number would be somewhere on the right side of the block, either by the starter, or down low by the fuel pump.
I have a '54 1/2-ton engine in my '53 6400, and it too has the earlier style valve cover. It's possible to put the early cover on the '54+ heads. Either someone was trying to disguise the engine as a '53, or they just didn't have a 4-bolt cover when the swap was done.
