I'm surprised no-ones mentioned the 200 '94xx' 0-6-0 steam tanks ordered by the Great Western from private builders in 1947, the last of which weren't delivered until 1956 - more than 20 years after the LMS had stopped building steam 0-6-0s in favour of diesels
Underframes for Southern Railway coaches of Bulleid design were (I think) constructed during the war but were not bodied until much later. In the interim, they were stored in the open.