Let me try ...
CASTING ID NOS. can be confusing but once the system(s) is understood, it begins to make sense.
During this period (50's roughly) FORD identified it's engines by a three character code, use EBU (1954 239 CI) for example.
These SERIES CODES (I am guessing on this term here) is also used as an ENGINEERING PART NUMBER PREFIX) to ID cast parts released for assembly/service.
So what you see is a three character prefix (again using EBU for reference), the ENGINEERING PN Basic PN (which will usually differ from SERVICE BASIC PART NUMBERS - example 6090 is the ENGINEERING BASIC PN and 6049 is the SERVICE BASIC PN for a bare cylinder head. Most ENGINEERING PN's can be converted to SERVICE PN's using FORD TEXT. The BASIC PN is not always shown on the actual part. The PN SUFFIX LETTER(s) gives more information.
The F surrounded by a C identifies the CASTING PLANT, in this instance CLEVELAND. There should also be somewhere the CASTING DATE CODE. The clockwork ID you see refers to what shift in the plant actually cast the part and gives more concise info than the CASTING DATE ID.
The other character(s) (X for instance) is a reference used in the foundry. It may or may not have a bearing on the casting as released for assembly/service.
The TECH SITE you showed refers to ID data mainly for the sixties/seventies era.
It is really not that confusing but now you see what a NUMBERS CORRECT restoration goes through.
Anything else, just ask.
NOTE: I made a few corrections to hopefully clarify. Did this help or not? If not, I will leave it alone.
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