The part of Mayo moved to Sligo shown here has not yet been recorded on the OSM data. It is difficult to identify candidate townland boundaries which would approximate this change.
Using the Memorial Atlas it looks as if these were predominantly townlands in 2 civil parishes. The boundary has been aligned along the parish boundaries. It remains to check this against the sketch map from Webb.
The part of Mayo moved to Sligo shown here has not yet been recorded on the OSM data. It is difficult to identify candidate townland boundaries which would approximate this change.