We are talking a 350-400 hp engine here. Plus no oversize stated. A very common situation.
Yes, weak cylinder walls can be found in production blocks and old blocks. I have had new blocks sonic checked and still unusable from sand/air inclusions (one a mexican block from Summit). Just had a 283 from an old boat checked and it was junk from massive corrosion in water side of cylinder walls .
But, for the average guy building a 350 street engine. I will not insist on sonic check.. If I did. I would have been out of business 45 years ago..