This is bullshit....
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Thin wall castings?
False. The later blocks have been found to be as thick or thicker than earlier blocks. The later blocks did have less nickel in them and were a little softer but they were still fine. Larry Shephard may have put out some good information but the "thin wall" stuff is wrong.
Why do you think you need to go .060 over? Where are you now? If you're at .030, why not take it .040? My '74 440 block is .040 over. Many 440 blocks have gone .060 without trouble, a 383 should too.
As stated before, a sonic check is the way to go. It will determine the thickness of the cylinders before you go any further.