The 350's & 455's aren't a problem.
It's the late 75 to 79 400 blocks that have the issue. Do a search on here and you will see pics of the difference between the early and later 400 block.
But 350 hp won't be a problem with the 557 block. I would make sure it has solid dowels in the mains and bottom fill it. Deburr any flashing or casting lines to remove stress risers. Keep the bore to .030 or .040 max.
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