Looks like a Ithaca made gun using parts on hand to make up alter grade gun. Serial number is only the most basic guide for Lefever production date. I have seen late features on early serial numbers but not early features on later guns. Use to think that was just from guns being returned to the factory and being upgraded to late features. Not so sure much if any of that occurred. I have a DS which has a burl stock which would have been at home on a A grade. Either a bin clean out gun or gun made for employee.
Remington employees use to raid the wood room for employee grade blanks all the time. I bought an 1100 Skeet with exhibition grade feather crotch from a retired Remington employee. Sure that type of thing has gone on forever.
