The last Emeryson 500cc was made in 1952 AFAIK, they have later switched to other classes. This one indeed looks like 1952 car, but with some new body panels (front aero and 'sidepods' with longer exhaust pipes). I'd still say it could be a pre-1955 model (I'm thinking of 1952 model now), possibly privately modified by someone in, say, 1956...