You might want to read this paper on Brinell hardness for OEM Blocks.
http://www.afsinc.org/files/images/iron%20alloys.pdf
From what I read 180 barely meets the bottom spec for a cast iron OEM block as far as material strength.
But you still would have a block with 4 bolt mains, (steel caps and splayed outer bolts), thicker cylinder walls, more material in the valley, stronger lifter bore design, etc.
Some years ago a Pontiac family bought some blocks that were not quite up to spec and eventually both blocks had issues, Failed.
That being said, Marty Palbykin (with a 1967 factory block) with splayed caps installed and some block chryo treatment ran a 1600 hp Twin Turbo engine for 3 years before a crack developed. Is the engine NA and what rpm are you assuming?
Tom V.