I just measured another 360 block I have in my garage. From the top it is exactly 7 1/2".
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You can see here the mark on my 408 is 1/2" from going in on the 360 block I measured. :
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Measured from the bottom:
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2 1/4" inches:
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Could this be a problem? Do I need to tap that oil plug in my 408 up from the main cap side a 1/2"?