Don't take anyone's word on anything- mic the bores yourself before exchanging money.
If the bores and the pistons both measure out at 4.070, you're bordering on an interference fit- zero clearance. No room for expansion of any kind.
Sounds like the block was rough bored/honed and still needs to be finished to size. Take the block and pistons to your machinist and have the bores finished to KB's specs for your pistons.
