Im using drop in pistons you think their no machine work needed your wrong, when using forged pistons thay require more piston to wall clearance than stock cause the expantion rate is greater cause they are forged. so they require you to take out about .002 to .004 out depending on cylinder size

and as for trusting a machine shop once you get the block back you should still measure for cylinder taper and for out of round with a dial bore gauge whitch is pretty simple and for honing you can do that yourself with a ball hone pistons come with a spec sheet that says the angle of cross hatch