This image from the actually captures the keystone! Way over at the left 4 keystones can be seen. The LPA has a great zoom, use that and you can see that there are two identical pairs: each with a male and a female head, and the male head is our friend, Pigtails.
is another photo which shows these buildings better but is less good at the details of the keystones. It shows a run of 4 neo-Georgian style buildings, facing onto Black Friars Lane, between Apothecaries Hall and what is now (2025) the yellow brick Keith Burns building, 81 Carter Lane. That's exactly the frontage now occupied by the extensive Cobham House, and on this it was occupied by 'Mill House' and the curved 'D'welling immediately south.
The photos are dated 1967/8 and the 4 houses are probably 1950s.
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