Cut off line for Cast and stock internals

What's the general census on cast internals & some stock parts (crank for example) at "x" boost before the need to upgrade to better internals?

The creature in question is a '69 340 Short Block with 60 over Keith Black Hyperereutic pistons, Stock forged crank, stock rods. (rotating assembly hasn't been balanced yet) Never assembled, getting the engine in trade for doing work to a friend's car.

Figured the Block & Crank would be a good starting platform for a mild Supercharged 340 to stick in one of my A-bodies. Don't know about the pistons, compression ratio is probably too high on them to use for the build. But is there a certain point where cast pistons are ok to use, or is it one of those deals where I should just get Forged pistons anyway?

Figured I'd keep the boost somewhat low and reasonable, Street Car. No need to go hogwild on exotic parts or an extremely radical engine