(With apologies for the delay in posting these photos)
These buses were being run by the Amersham & District Motorbus Society. They organise several events during the year and Chesham Bus Running Day, which is an annual event held this year, on the 1st October 2023.
The Pic of MXX313 (photo below) is numbered GS13 which is a 1953 Guy Special.
The Pic of NLE673 is a Metro-Cammell bodied AEC Regal IV, typical of the type used for Greenline services.
The nearest route that did exist was the 709 Godstone to Chesham. More photos on bellingdon.com