The current ICAO (International Civil Aviation Organization) identifier for the Fort MacLeod airport is CEY3. Sorry, but I don't have information on the period identifier. ICAO is a postwar creation (1947) so there may not be any linkage between the airport designators then and now. But, if you are lucky, they might just have added the C at the beginning to identify Canada.
Looking at the satellite image at
https://www.google.com/maps/place/Fo...4d-113.4147974 the current airport is clearly on the site of the BCATP airport.