Mel,
It looks like it's 51-4754.
See page 80 of
Cessna Warbirds: A Detailed & Personal History of Cessna's Involvement in the Armed Forces by Walt Shiel, Gregory W. Bayer, Frank Hamilton, Kim Shields.
Google ("l-19" raf korea). The whole book is online.
By October 1954, Cessna deliveries of L-19s totaled 2,504 aircraft. Five aircraft were destined for service in the South Korean air force under the Military Assistance program and one (L-19-ACE, s/n 51-4754) was obtained by the British Army from the Canadian Army.
Adjacent to the text is a US Army Aviation Museum photo of 51-4754 with roundels, captioned
A Canadian L-19A-CE flown by the British RAF (sic) out of Seoul, South Korea in 1952