Depends on the specific engine these would be for,and the specific 4x heads in question,there are like a half dozen different variations of the 4x castings,each with it's own pluses and minuses.
Other than that,reports suggest the 4x castings are more prone to cracking than the later 5c and 6x castings,so magnafluxing any potential castings is mandatory.
But that should be the case with all castings regardless...
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