That particular "Mortar", has to be original, and listed as a "C&R" in either the "C&R-List"....or the up-dated part that BATF adds to awaiting to "up-date" the C&R List (Book).
IE: If the gun is not listed in the C&R List.......then you have to either have it added to the C&R List (to be able to transfer it to you on your C&R License)....or transfer it like you would through a local Class-III Dealer in your state.
Some additional information from the 4467 may help to determine who the manufacturer was/is........then to check the C&R List.
Regards, RichardS in MI.
US Army, RetiredBlanksguy2001@chartermi.net