Machining a block, how it´s going???

a machinist that takes pride in his work and reputation will want both pistons and rings. DIfferent rings require different bore finishes.
Now about overbore... metals , including cast iron will expand and contract with temperture change.Some more than others. The cylinder wall needs to ne thick enough to keep this change as round as possible. The problem with oversize boring comes from the lack of wall thickness at the water jackets.
Uneven cylinder wall temperture equals uneven expansion.