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Thank you Dave. My head doesn't have any numbers there. I am starting to think it is a 29 head.The temperature gauge hole is not in the back of the head. All my head says is MADE IN USA and C4 MF. What do you think?
I agree with Gene, without the bow tie and Chevrolet part number it must be aftermarket. I looked at 4 more heads and three had part numbers as pictured. The fourth head just has an intertwined C and L in the center.
That definitely looks like a Chevy head casting for a 1930-31. My best guess is that the "X" is an indicator of which pattern was used for that casting.
That is a very normal practice in the casting and forging industries when multiple patterns or dies are used. It helped them track the source of problems.
Sometimes an extra letter or symbol is used for parts are are produced for the parts system by either the original supplier or another. Look for the casting date to see if it might be cast a few years later?
The casting dates of the two heads without the X are mid 1930. The heads with the X are both cast in 1931. Maybe something as suggested in a change of pattern but they were pretty good at changing part numbers for changes in parts without a lot of provocation.