> There were a number of gauge changes, but they were usually quite early on, when the infra was less critical and you could get away with closing lines for months.
It was also a time when railways used wooden sleepers, so you could simply drill new holes at the new track gauge for moving the rail fasteners, thereby minimising the work required for changing the gauge, at least on the plain line, switches and crossings excepted.
Plus it was a time when a lot more manpower for that kind of massive manual work was available, plus railways were the dominant transport mode and could actually commandeer that kind of manpower.
It was also a time when railways used wooden sleepers, so you could simply drill new holes at the new track gauge for moving the rail fasteners, thereby minimising the work required for changing the gauge, at least on the plain line, switches and crossings excepted.
Plus it was a time when a lot more manpower for that kind of massive manual work was available, plus railways were the dominant transport mode and could actually commandeer that kind of manpower.