I the days that these were designed cases were meant to be cut 0.25mm or maximum 0.5 mm and the reamer for the small bearing (closest to the pulley) was meant to cut the pulley bore as well hence the need for an oversized pulley. Both things not easy to achieve with a worn reamer. The reamers were adjustable and relied heavily on operator skills to ensure that they cut the correct size hole and make that hole round.
One Rand could buy two american dollars those days and getting a set of Hunger reamers were easy and semi affordable They would pay for themselfes within ten engines and were state of the art in the sixties.
Line boring of beetle engines used to be done by every jan rap en sy maat back in the old days.
