The 1950s maps used to be online , but the site closed down , as they decided they were not making enough money from it. Some members saved areas of it before it closed down, and in the future hopefully it will be available from the National Library of Scotland website, which at present only has Scotland, London and a few parts of the south of England, but is planning to expand the cover.
The map you refer to shows no 139 in red. A little below it no 123 is marked on the original map. No 121 is the house just below 123