If the engine number just has the W in the prefix it represents a low compression 45. None are listed for US production but there have been others appear that were for export. Very little info exist for export models but search this forum for more info. Some South American and Asian countries ordered 45s for various duties. I would consider it a very rare piece if the numbers are an authentic stamping. But despite your description, without pictures it is impossible to tell if the numbers are original or just stamped on Military surplus blank cases.
So no pictures, no proof!