I haven't seen new images of converted vehicles turned into rail cars in quite a while, but then I found this Flikr account yesterday, and bingo! Several that the british converted in the 20's and 30's

British Army railroad vehicles/trollies with machine-guns landed from the S.S. Dorsetshire in Palestine - circa 1936
https://www.flickr.com/photos/39411748@N06/6135139683/