Before going hog-wild in an effort to either clean up worn cylinder bores or to over-bore for increased displacement, it’s critical to first determine cylinder wall thickness (meaning the thickness of the wall area opposite cooling jackets).
Generally speaking, for a high-performance build, the thinnest recommended final cylinder bore wall should be at least approximately 0.200-in. thick.
If the wall is too thin, excess cylinder bore distortion can occur, leading to either poor ring sealing or cylinder wall cracking.
The higher the compression ratio, or if additional cylinder pressure is planned (via nitrous injection, turbocharging or supercharging), the more critical wall thickness becomes.
Don’t guess at this. Obtain accurate measurement using a properly calibrated sonic wall-thickness gauge before you invest time and expense in block machining.