1974 426 Hemi block question?

I have a 1974 426 Hemi block that has the correct part# cast into as well as an X cast off to the side of the part #. Can anyone tell me or point me to a source to identify what the deal is with this block? I've been told that it's a warranty block by one guy and another said it could be a factory block for the top fuel cars. Any help appreciated!

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