302 heads and cracking

What do they mean about this circled? I can hit my boneyard today and get a vin off a junker if need be, unless somebody has a "pet vin" they would like to share with me. These will be $615 shipped to my doorstep. Not bad really. Saves me from having to break my balls in the boneyard getting an uncracked set. I would like to hit the buy button now.

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