I have just discovered an addition last month to the National Library of Scotland mapping website. They have created a seamless layer from the sheets of the OS first edition 6 inch to 1 mile, which is c1850 in Yorkshire. You can also now display this side by side with a c1901 revision. This example shows the Park area where we were trying to identify High Street, Park, which the maps show was renamed Bard Street. You can drag it to another position.