Mine is seven numbers before yours, 500,884, shipped April 17, 1941. Mine is a non ejector Field Grade with unusual hard butt, and sling swivels that appear to be factory. Ithaca seems to be the only American shotgun company that regularly installed swivels. My gun doesn't appear to have ever gone hunting. These are some great guns. Maybe I misread your serial number. In the picture, the 6 looked like an 8. Oh, well.