A snapshot taken by a relative of mine, probably in the mid 1960's. ( I'm asuming this is Seaton Sluice)

It is indeed, Seaton Sluice Old Bridge. The new bridge was completed in 1968 so you are probably about right on the date it was taken. Crossed the burn via the pipe many a time when we were kids.

An earlier view of the other side and the new bridge under construction.