On my '57 the engine number appears also on the right frame rail ahead the wheel opening (aprox. under the rear door if you've a 4dr). Perhaps hidden by the gas line (and paint..). I think ther's a pic of the location in the '57 IML page -- Philippe COURANT (Pau, France) Imperial 57 Crown convertible Buick 58 Roadmaster sedan - American Car Club de France (ACCF) : http://www.accf.com - Chrysler Imperial France : http://www.ifrance.com/c-i-f - Cadillac " Standard of Excellence " : http://www.ifrance.com/accf-cad - SportsCars : http://www.ifrance.com/accf-sprtcar