As far as I can tell from my 1935-55 Master Parts List, a '54 coupe's door latches are part number 466 3638 for the right latch and 466 3639 for the left. It does not interchange with any other '54 latch, but does interchange with early '55 coupes, sedans, limos and convertibles. It does not interchange with the '55 Fleetwood 60S. (This does not make total sense to me, but that is what the MPL says.)
The MPL doesn't mention other GM makes, but I know in some other years, including '49, Buick Super and Roadmaster door latches interchange with Cadillac.
