Been thinking about the Butler response to this condition being core shift and that being dismissed out of hand by everyone in the thread. While I agree a machining error in tang location or the crankshaft is the most likely cause, IMO core shift is a possibility. Here is how. The main saddles are part of the multiple cores assembled in the core box for the block. During the pour of there was a minor shift in the core box, one or more of the main saddles could be slightly out of position. When it was originally line bored and assembled with a cast OE crankshaft with almost no fillet radius it may have just barely cleared and run without issue. When the Scat crank was installed with the large radius, everything changed as far as fitment and minimum clearance and then the failure. So , I am saying core shift is possible. It's something I have never seen in the #5 of a Pontiac, but I learn new things every day. I will sure be looking more carefully in that area now.
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